ALBERT

Description: Mucus, a complex composed primarily of carbohydrates, is released in similar quantities by scleractinian warm- and cold-water reef corals, and can function as an important carrier of organic material from corals to a range of consumers, microbes in particular. However, information about mucus chemical composition is rare for warm-water corals and non-existent for cold-water corals. This study therefore presents comparative carbohydrate composition analyses of mucus released by the dominant and cosmopolitan warm- and cold-water coral genera. Arabinose was the major mucus carbohydrate component for the genus Acropora, but was not found in cold-water coral mucus. Mucus derived from corals of the genus Fungia contained significantly more fucose than the mucus of all other coral genera. However, comparison of mucus carbohydrate composition for the warm- and cold-water corals in the present study and in the literature revealed no significant differences. This indicates use of similar carbohydrate components (with the exception of arabinose) during mucus synthesis by scleractinian corals, largely irrespective of zooxanthellate or azooxanthellate carbon supply mechanisms.

Description: Multichannel seismic reflection data were used to determine the evolutionary history of the forearc region of the central Aleutian Ridge. Since at least late Miocene time this sector of the ridge has been obliquely underthrust 30° west of orthogonal convergence by the northwestward converging Pacific plate at a rate of 80–90 km/m.y. Our data indicate that prior to late Eocene time the forearc region was composed of rocks of the arc massif thinly mantled by slope deposits; the forearc region probably lacked both major depositional basins and a tectonically attached accretionary prism of offscraped oceanic deposits. Beginning in latest Miocene or earliest Pliocene time, a zone of outer-arc structural highs and a forearc basin began to form. Formation of these companion intraarc structures may be linked to the late Neogene growth of an accretionary wedge that formed as the result of the deposition of a thick turbidite wedge in the Aleutian Trench. Initial structures of the zone of outer-arc highs formed as the thickening wedge underran, compressively deformed, and uplifted the seaward edge of the arc massif above a landward dipping backstop thrust. Forearc basin strata ponded arcward of the elevating zone of outer-arc highs. However, most younger structures of the zone of outer-arc highs cannot be ascribed simply to the orthogonal effects of an underrunning wedge. Oblique convergence created a major right-lateral shear zone (the Hawley Ridge shear zone) that longitudinally disrupted the zone of outer-arc highs, truncating the seaward flank of the forearc basin and shearing the southern limb of Hawley Ridge, an exceptionally large antiformal outer-arc high structure. Slivers of forearc basement rocks and overlying strata have been transported along the shear zone that is flanked by differentially elevated structures attributed to localized transpressive and transtensional processes. Uplift of Hawley Ridge may be related to the thickening of the arc massif by westward directed basement duplexes. In addition, the forearc is disrupted by structures transverse to the margin that occur where unusually high-stress accumulations have resulted in the rupture of repeated great earthquakes. It is likely that many ancient active margins evolved in tectonic and depositional settings similar to those of the central Aleutian Ridge. Great structural complexity, including the close juxtaposition of coeval structures recording compression, extension, differential vertical movements, and strike-slip displacement, should be expected, even within areas of generally kindred tectonostratigraphic terranes.

Description: Mixing processes of reduced hydrothermal fluids with oxygenated seawater and fluid-rock reactions contribute to the chemical signatures of diffuse venting and likely determine the geochemical constraints on microbial life. We examined the influence of fluid chemistry on microbial diversity and activity by sampling diffuse fluids emanating through mussel beds at two contrasting hydrothermal vents. The H(2) concentration was very low at the basalt-hosted Clueless site, and mixing models suggest O(2) availability throughout much of the habitat. In contrast, effluents from the ultramafic-hosted Quest site were considerably enriched in H(2) , while O(2) is likely limited to the mussel layer. Only two different hydrogenase genes were identified in clone libraries from the H(2) -poor Clueless fluids, but these fluids exhibited the highest H(2) uptake rates in H(2) -spiked incubations (oxic conditions, at 18 °C). In contrast, a phylogenetically diverse H(2) -oxidizing potential was associated with distinct thermal conditions in the H(2) -rich Quest fluids, but under oxic conditions, H(2) uptake rates were extremely low. Significant stimulation of CO(2) fixation rates by H(2) addition was solely illustrated in Quest incubations (P-value 〈0.02), but only in conjunction with anoxic conditions (at 18 °C). We conclude that the factors contributing toward differences in the diversity and activity of H(2) oxidizers at these sites include H(2) and O(2) availability.

Description: Much attention has been paid, in recent years, to the potential application of the Ce anomaly, measured in various marine phases, as a paleoceanographic indicator of widespread marine anoxia. In this paper we present and discuss results from recent studies of present‐day rare earth element (REE) distributions (and hence Ce anomaly distributions) in the marine environment which are particularly pertinent to paleoceanography. Subsequently, we review and discuss the validity of the recent literature in which Ce anomalies have been employed as paleoredox indicators.

Description: Abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical Atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected. As expected from previous work in the tropics, all dominant tropical species occur in greatest abundance within the photic zone. Many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration, while a few algal symbiont-bearing species occur in greatest abundance in the mixed layer. The δ18O measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by Ravelo et al. [1990]. Comparison between the measured δ18O values of planktonic foraminifera with the predicted δ18O profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year. Species which calcify below the photic zone have only trace relative abundances. Finally, it appears that the total range of δ18O values of the dominant species approximates the predicted annual δ18O of calcite range in the upper 80 m of the water column.

Description: Previous studies have suggested that phytoplankton play an important role in the biogeochemical cycling of iodine, due to the appearance of iodide in the euphotic zone. Changes in the speciation of iodine over the course of the growth cycle were examined in culture media for a variety of phytoplankton taxa (diatoms, dinoflagellates and prymnesiophytes). All species tested showed the apparent ability to reduce iodate to iodide, though production rates varied considerably between species (0.01 to 0.26 nmol l–1 µg–1 chl a d–1), with Eucampia antarctica the least and Pseudo-nitzschia turgiduloides the most efficient iodide producers. Production was found to be species specific and was not related to biomass (indicated by e.g. cell size, cell volume, or chl a content). In all species, except for the mixotrophic dinoflagellate Scrippsiella trochoidea, iodide production commenced in the stationary growth phase and peaked in the senescent phase of the algae, indicating that iodide production is connected to cell senescence. This suggests that iodate reduction results from increased cell permeability, which we hypothesize is due to subsequent reactions of iodate with reduced sulphur species exuded from the cell. A shift from senescence back to the exponential growth phase resulted in a decline in iodide and indicated that phytoplankton-mediated oxidation of iodide to iodate was likely to be occurring. Iodide production could not be observed in healthy cells kept in the dark for short periods. Bacterial processes appeared to play only a minor role in the reduction of iodate to iodide.

Description: The Mauritanian coastal area is one of the most biologically productive upwelling regions in the world ocean. Shipboard observations carried out during maximum upwelling season and short-term moored observations are used to investigate diapycnal mixing processes and to quantify diapycnal fluxes of nutrients. The observations indicate strong tide-topography interactions that are favored by near-critical angles occurring on large parts of the continental slope. Moored velocity observations reveal the existence of highly nonlinear internal waves and bores and levels of internal wave spectra are strongly elevated near the buoyancy frequency. Dissipation rates of turbulent kinetic energy at the slope and shelf determined from microstructure measurements in the upper 200 m averages to ɛ = 5 × 10−8 W kg−1. Particularly elevated dissipation rates were found at the continental slope close to the shelf break, being enhanced by a factor of 100 to 1000 compared to dissipation rates farther offshore. Vertically integrated dissipation rates per unit volume are strongest at the upper continental slope reaching values of up to 30 mW m−2. A comparison of fine-scale parameterizations of turbulent dissipation rates for shelf regions and the open ocean to the measured dissipation rates indicates deficiencies in reproducing the observations. Diapycnal nitrate fluxes above the continental slope at the base of the mixed layer yielding a mean value of 12 × 10−2 μmol m−2 s−1 are amongst the largest published to date. However, they seem to only represent a minor contribution (10% to 25%) to the net community production in the upwelling region.

Description: The importance of the Gulf Stream Extension region in climate and seasonal prediction research is being increasingly recognised. Here we use satellite-derived eddy momentum fluxes to drive a shallow water model for the North Atlantic Ocean that includes the realistic ocean bottom topography. The results show that the eddy momentum fluxes can drive significant transport, sufficient to explain the observed increase in transport of the Gulf Stream following its separation from the coast at Cape Hatteras, as well as the observed recirculation gyres. The model also captures recirculating gyres seen in the mean sea surface height field within the North Atlantic Current system east of the Grand Banks of Newfoundland, including a representation of the Mann Eddy.

Description: A decade of weak convection in the Labrador Sea associated with decreasing water mass transformation, in combination with advective and eddy fluxes into the convection area, caused significant warming of the deep waters in both the central Labrador Sea and boundary current system along the Labrador shelf break. The connection to the export of Deep Water was studied based on moored current meter stations between 1997 and 2009 at the exit of the Labrador Sea, near the shelf break at 5˚3N. More than 100 year -long current meter records spanning the full water column have been analyzed with respect to high frequency variability, decaying from the surface to the bottom layer, and for the annual mean flow, showing intra- to interannual variability but no detectable decadal trend in the strength of the deep and near-bottom flow out of the Labrador Sea.

Description: Recent work shows that multichannel seismic (MCS) systems provide detailed information on the oceans' finestructure. The aim of this paper is to analyze if high order numerical algorithms are suitable to accurately model the extremely weak wavefield scattered by the oceans' finestructures. For this purpose, we generate synthetic shot records along a coincident seismic and oceanographic profile acquired across a Mediterranean salt lens in the Gulf of Cadiz. We apply a 2D finite-difference time-domain propagation model, together with second-order Complex Frequency Shifted Perfectly Matched Layers at the numerical boundaries, using as reference a realistic sound speed map with the lateral resolution of the seismic data. We show that our numerical propagator creates an acoustical image of the ocean finestructures including the salt lens that reproduces with outstanding detail the real acquired one

Description: Recently seismic reflection methods have been successfully applied to oceanographic issues. Here, we present a new approach, combining XBT and CTD surveys with seismic observations, to visualize long sections with a resolution down to a few meters. The challenge to a full investigation of mixing processes has been the tremendous span of spatial scales ranging from hundreds of kilometers to centimeters. Traditional hydrographic observations could only resolve the large scale effects by measuring temperature and salinity profiles at discrete locations typically several kilometers apart, whereas dedicated localized measurements allowed investigation of the ocean fine structure at the other end of the spatial spectrum. The intermediate scales have in contrast been difficult to observe systematically. Here we present temperature and salinity data inverted from seismic observations that cover the intermediate scales and provide a new approach to image mesoscale processes and allow the investigation of their dynamics at unprecedented resolution.

Description: Nitrogen (N) fixation by specialized microorganisms (diazotrophs) influences global plankton productivity because it provides the ocean with most of its bio-available N. However, its global rate and large-scale spatial distribution is still regarded with considerable uncertainty. Here we use a global ocean nitrogen isotope model, in comparison with δ15NO3− observations, to constrain the pattern of N2 fixation across the Pacific Ocean. N2 fixation introduces isotopically light atmospheric N2 from to the ocean (δ15N = 0‰) relative to the oceanic average near 5‰, which makes nitrogen isotopes suitable to infer patterns of N2 fixation. Including atmospheric iron limitation of diazotrophy in the model shifts the pattern of simulated N2 fixation from the South Pacific to the North Pacific and from the East Pacific westward. These changes considerably improve the agreement with meridional transects of available δ15NO3− observations, as well as excess P (PO43− − NO3−/16), suggesting that atmospheric iron deposition is indeed important for N fixation in the Pacific Ocean. This study highlights the potential for using δ15N observations and model simulations to constrain patterns and rates of N fixation in the ocean.

Description: The Atlantic‐Mediterranean exchange of water at Gibraltar represents a significant heat and freshwater sink for the North Atlantic and is a major control on the heat, salt and freshwater budgets of the Mediterranean Sea. Consequently, an understanding of the response of the exchange system to external changes is vital to a full comprehension of the hydrographic responses in both ocean basins. Here, we use a synthesis of empirical (oxygen isotope, planktonic foraminiferal assemblage) and modeling (analytical and general circulation) approaches to investigate the response of the Gibraltar Exchange system to Atlantic freshening during Heinrich Stadials (HSs). HSs display relatively flat W–E surface hydrographic gradients more comparable to the Late Holocene than the Last Glacial Maximum. This is significant, as it implies a similar state of surface circulation during these periods and a different state during the Last Glacial Maximum. During HS1, the gradient may have collapsed altogether, implying very strong water column stratification and a single thermal and d18Owater condition in surface water extending from southern Portugal to the eastern Alboran Sea. Together, these observations imply that inflow of Atlantic water into the Mediterranean was significantly increased during HS periods compared to background glacial conditions. Modeling efforts confirm that this is a predictable consequence of freshening North Atlantic surface water with iceberg meltwater and indicate that the enhanced exchange condition would last until the cessation of anomalous freshwater supply into to the northern North Atlantic. The close coupling of dynamics at Gibraltar Exchange with the Atlantic freshwater system provides an explanation for observations of increased Mediterranean Outflow activity during HS periods and also during the last deglaciation. This coupling is also significant to global ocean dynamics, as it causes density enhancement of the Atlantic water column via the Gibraltar Exchange to be inversely related to North Atlantic surface salinity. Consequently, Mediterranean enhancement of the Atlantic Meridional Overturning Circulation will be greatest when the overturning itself is at its weakest, a potentially critical negative feedback to Atlantic buoyancy change during times of ice sheet collapse.

Description: The phosphorus budget of the pre-human modern ocean is constrained applying the most recent estimates of the natural riverine, eolian, and ice-rafted input fluxes, the phosphorus burial in marine sediments, and the hydrothermal removal of dissolved phosphate from the deep ocean. This review of current flux estimates indicates that the phosphorus budget of the ocean is unbalanced since the accumulation of phosphorus in marine sediments and altered oceanic crust exceeds the continental input of particulate and dissolved phosphorus. The phosphorus mass balance is further tested considering the dissolved phosphate distribution in the deep water column, the marine export production of particulate organic matter, rain rates of phosphorus to the seafloor, benthic dissolved phosphate fluxes, and the organic carbon to phosphorus ratios in marine particles. These independent data confirm that the phosphate and phosphorus budgets were not at steadystate in the pre-human global ocean. The ocean is losing dissolved phosphate at a rate of ≥ 11.6 x 1010 mol yr-1 corresponding to a decline in the phosphate inventory of ≥ 4.5 % kyr-1. Benthic data show that phosphate is preferentially retained in pelagic deep-sea sediments where extended oxygen exposure times favor the degradation of particulate organic matter and the up-take of phosphate in manganese and iron oxides and hydroxides. Enhanced C : P regeneration ratios observed in the deep water column (〉400 m water depth) probably reflect the preferential burial of phosphorus in pelagic sediments. Excess phosphate is released from continental margin sediments deposited in low-oxygen environments. The dissolved oxygen threshold value for the enhanced release of dissolved phosphate is ~20 μM. Benthic phosphate fluxes increase drastically when oxygen concentrations fall below this value.

Description: The decay kinetics of superoxide (O2−) reacting with organic matter was examined in oligotrophic waters at, and nearby, the TENATSO ocean observatory adjacent to the Cape Verde archipelago. Superoxide is the short-lived primary photochemical product of colored dissolved organic matter (CDOM) photolysis and also reacts with CDOM or trace metals (Cu, Fe) to form H2O2. In the present work we focused our investigations on reactions between CDOM and superoxide. O2− decay kinetics experiments were performed by adding KO2 to diethylenetriaminepentaacetic acid (DTPA) amended seawater and utilizing an established chemiluminescence technique for the detection of O2− at nM levels. In Cape Verdean waters we found a significant reactivity of superoxide with CDOM with maximal rates adjacent to the chlorophyll maximum, presumably from production of new CDOM from bacteria/phytoplankton. This work highlights a poorly understood process which impacts on the biogeochemical cycling of CDOM and trace metals in the open ocean.

Description: We determined methane (CH4) emissions in a field enclosure experiment in a littoral freshwater marsh under the influence of experimentally simulated warming and enhanced nitrogen deposition. Methane emissions by ebullition from the marsh composed of Phragmites australis were measured with funnel traps deployed in a series of enclosures for two 3 week periods. Diffusive fluxes were estimated on the basis of measured CH4 concentrations and application of Fick's law. Neither diffusive nor ebullitive fluxes of methane were significantly affected by warming or nitrate enrichment, possibly because variability both within and among replicate experimental enclosures was high. Average emission rates resulted primarily from ebullition (0.2–30.3 mmol CH4 m−2 d−1), which were 4 orders of magnitude higher than estimated diffusive fluxes and were of similar importance as the coarsely estimated advective methane transport through plants. Significant correlations between dissolved oxygen and dissolved methane and ebullition flux suggest that methane release from the sediment might feed back positively on methane production by reducing dissolved oxygen in the water column and oxygen flux into the sediment. Nitrate may have a similar effect. Extrapolation of our limited data indicates that total methane fluxes from vegetated littoral zones of temperate lakes may contribute 0.5%–7% of the global natural CH4 emissions. These results emphasize the importance of freshwater marshes as sources of methane emissions to the atmosphere, even when they occupy only relatively small littoral areas. More detailed investigations are clearly needed to assess whether global warming and nitrogen deposition can have climate feedbacks by altering methane fluxes from these wetlands.

Description: The sensitivity of the hydrological cycle to changes in orbital forcing and atmospheric greenhouse gas (GHG) concentrations is assessed using a fully coupled atmosphere-ocean-sea ice general circulation model (Kiel Climate Model). An orbitally-induced intensification of the summer monsoon circulation during the Holocene and Eemian drives enhanced water vapor advection into the Northern Hemisphere, thereby enhancing the rate of water vapor changes by about 30% relative to the rate given by the Clausius-Clapeyron Equation, assuming constant relative humidity. Orbitally-induced changes in hemispheric-mean precipitation are fully attributed to inter-hemispheric water vapor exchange in contrast to a GHG forced warming, where enhanced precipitation is caused by increased both the moisture advection and evaporation. When considering the future climate on millennial time scales, both forcings combined are expected to exert a strong effect.

Description: We present results from a seismic refraction and wide-angle experiment surveying an oceanic core complex on the Mid-Atlantic Ridge at 22°19′N. Oceanic core complexes are settings where petrological sampling found exposed lower crustal and upper mantle rocks, exhumed by asymmetric crustal accretion involving detachment faulting at magmatically starved ridge sections. Tomographic inversion of our seismic data yielded lateral variations of P wave velocity within the upper 3 to 4 km of the lithosphere across the median valley. A joint modeling procedure of seismic P wave travel times and marine gravity field data was used to constrain crustal thickness variations and the structure of the uppermost mantle. A gradual increase of seismic velocities from the median valley to the east is connected to aging of the oceanic crust, while a rapid change of seismic velocities at the western ridge flank indicates profound differences in lithology between conjugated ridge flanks, caused by un-roofing lower crust rocks. Under the core complex crust is approximately 40% thinner than in the median valley and under the conjugated eastern flank. Clear PmP reflections turning under the western ridge flank suggest the creation of a Moho boundary and hence continuous magmatic accretion during core complex formation.

Description: The Mid-Atlantic Ridge south of the equator is a key region for many aspects of spreading axis studies, from biogeography to ridge-hotspot interaction. Despite this, the ridge axis had, until 2004, seen little systematic study. Repeated trips to the area since then have mapped and explored some 900 km of ridge length, from 2° to 14°S. The result is complete bathymetric and side-scan coverage of the axial region and the discovery and characterization of the first hydrothermal vents south of the equator. Such multisegment detailed and interdisciplinary coverage allows us to formulate a general model for the interplay between volcanism, tectonics, and hydrothermalism on a slow spreading ridge. The model defines three basic types of ridge morphology with specific hydrothermal characteristics: (a) a deep, tectonically dominated rift valley where hydrothermalism is seldom associated with volcanism and much more likely confined to long-lived bounding faults; (b) a shallower, segment-center bulge where a combination of repeated magmatic activity and tectonism results in repeated, possibly temporally overlapping periods of hydrothermal activity on the ridge axis; and (c) a very shallow axis beneath which temperatures in all but the uppermost crust are so high that deformation is ductile, inhibiting the formation of high-porosity deep fractures and severely depressing hydrothermal circulation. This model is used together with satellitederived predicted bathymetry to provide forecasts of the best places to look for hydrothermal sites in the remaining unexplored regions of the South Atlantic.

Description: The Sahara Slide is a giant submarine landslide on the northwest African continental margin. The landslide is located on the open continental slope offshore arid Western Sahara, with a headwall at a water depth of ∼2000 m. High primary productivity in surface waters drives accumulation of thick fine-grained pelagic/hemipelagic sediment sequences in the slide source area. Rare but large-scale slope failures, such as the Sahara Slide that remobilized approximately 600 km3 of sediment, are characteristic of this sedimentological setting. Seismic profiles collected from the slide scar reveal a stepped profile with two 100 m high headwalls, suggesting that the slide occurred retrogressively as a slab-type failure. Sediment cores recovered from the slide deposit provide new insights into the process by which the slide eroded and entrained a volcaniclastic sand layer. When this layer was entrained at the base of the slide it became fluidized and resulted in low apparent friction, facilitating the exceptionally long runout of ∼900 km. The slide location appears to be controlled by the buried headwall of an older slope failure, and we suggest that the cause of the slide relates to differential sedimentation rates and compaction across these scarps, leading to local increases of pore pressure. Sediment cores yield a date of 50–60 ka for the main slide event, a period of global sea level rise which may have contributed to pore pressure buildup. The link with sea level rising is consistent with other submarine landslides on this margin, drawing attention to this potential hazard during global warming.

Description: Traditionally, consumer–prey interactions have been considered as purely negative, but herbivores may have positive effects on plants and their productivity. Grazing may enhance prey biomass-specific productivity by directly or indirectly reducing the competition for light, nutrients, and space. We studied the effect of 4 common mesograzers, the isopod Idotea baltica, the amphipod Gammarus oceanicus, and the gastropods Littorina littorea and Rissoa membranacea on epiphytes in an eelgrass Zostera marina L. system. Eelgrass was grown in laboratory mesocosms for a set of experiments manipulating mesograzer species identity, mesograzer density and nutrient concentration. We measured epiphyte biomass-specific productivity via incorporation of radioactive carbon. Herbivore effects on epiphyte photosynthetic capacity were strongly positive for R. membranacea, moderately positive for L. littorea and I. baltica and zero for G. oceanicus under low nutrient supply. Both gastropods increased the nitrogen content of epiphytes, especially the small R. membranacea, and enhanced epiphyte growth. The crustacean species did not increase epiphyte nutrient content, but I. baltica probably enhanced epiphyte productivity by removing the overstory of algal cells, and thus reducing competition for light, nutrients, and space. The positive effect of the 2 gastropod species disappeared under higher nutrient supply, implying the importance of nutrient limitation for this interaction. The positive effect of I. baltica remained at moderate grazer densities despite the higher nutrient concentrations.

Description: The supply of oxygen-rich water to the oxygen minimum zones (OMZs) of the eastern North and South Pacific via zonal tropical currents is investigated using shipboard acoustic Doppler current profiler and hydrographic section data. Near the equator, the Equatorial Undercurrent (EUC), Northern and Southern Subsurface Countercurrents (SCCs), and the Northern and Southern Intermediate Countercurrents (ICCs) all carry water that is oxygen richer than adjacent westward flows, thereby providing a net oxygen supply to the eastern Pacific OMZs. The synoptic velocity-weighted oxygen concentration difference between eastward and westward flows is typically 10–50 μmol kg−1. Subthermocline zonal oxygen fluxes reflect decreasing oxygen concentrations of the EUC, the SCCs, and the ICCs as they flow eastward. Approximately 30 year time series in well-sampled regions of the equatorial Pacific show oxygen content decreasing as rapidly as −0.55 μmol kg−1 yr−1 in the major oxygen supply paths of the OMZs for a 200–700 m layer and similar trends for a density layer spanning roughly these depths. This finding is in gross agreement with climate models, which generally predict expanding OMZs.

Description: Near the western boundary of the tropical North Atlantic, where the North Brazil Current (NBC) retroflects into the North Equatorial Countercurrent, large anticyclonic rings are shed. After separating from the retroflection region, the so-called NBC rings travel northwestward along the Brazilian coast, until they reach the island chain of the Lesser Antilles and disintegrate. These rings contribute substantially to the upper limb return flow of the Atlantic Meridional Overturning Circulation by carrying South Atlantic Water into the northern subtropical gyre. Their relevance for the northward transport of South Atlantic Water depends on the frequency of their generation as well as on their horizontal and vertical structure. The ring shedding and propagation and the complex interaction of the rings with the Lesser Antilles are investigated in the inline equation Family of Linked Atlantic Model Experiments (FLAME) model. The ring properties simulated in FLAME reach the upper limit of the observed rings in diameter and agree with recent observations on seasonal variability, which indicates a maximum shedding during the first half of the year. When the rings reach the shallow topography of the Lesser Antilles, they are trapped by the island triangle of St. Lucia, Barbados and Tobago and interact with the island chain. The model provides a resolution that is capable of resolving the complex topographic conditions at the islands and illuminates various possible fates for the water contained in the rings. It also reproduces laboratory experiments that indicate that both cyclones and anticyclones are formed after a ring passes through a topographic gap. Trajectories of artificial floats, which were inserted into the modeled velocity field, are used to investigate the pathways of the ring cores and their fate after they encounter the Lesser Antilles. The majority of the floats entered the Caribbean, while the northward Atlantic pathway was found to be of minor importance. No prominent pathway was found east of Barbados, where a ring could avoid the interaction with the islands and migrate toward the northern Lesser Antilles undisturbed.

Description: Previous studies on trait-mediated trophic interactions in marine ecosystems were restricted to pair-wise interactions between one species of meso-herbivore and plant, though multi-grazer interactions are more common in nature. We investigated whether the feeding of one consumer, either the periwinkle Littorina littorea or the isopod Idotea baltica, affected consumption by the other consumer via anti-herbivory defence induction in the brown seaweed Fucus vesiculosus. To test the generality of our findings, we ran similar experiments with seaweed/grazer populations in the North and Baltic Seas (NE Atlantic). Grazer-specificity in induction strength was assessed by using the same species of grazer for induction and consumption. ‘Indirect’ induction effects were assessed by using different species of grazers for induction and consumption. Palatability assays were run with live algae and with reconstituted food to distinguish between different mechanisms of resistance. Grazing by herbivores induced a chemical defence in F. vesiculosus. In the North Sea population, the induced defences were only effective against I. baltica, regardless of inducer identity. The sensitive responses of I. baltica to the induced defences were also detected in the reconstituted food assays using Baltic Sea organisms. Thus, marine meso-grazers may be affected by previous feeding through the same or a different species of consumer by modified prey traits, such as induced chemical defences. Furthermore, the magnitude of the effect in the induced defences can be determined by species-specific sensitivity.

Description: How multiple stressors influence fish stock dynamics is a crucial question in ecology in general and in fisheries science in particular. Using time-series covering a 30 yr period, we show that the body growth of the central Baltic Sea herring Clupea harengus, both in terms of condition and weight-at-age (WAA), has shifted from being mainly driven by hydro-climatic forces to an inter-specific density-dependent control. The shift in the mechanisms of regulation of herring growth is triggered by the abundance of sprat, the main food competitor for herring. Abundances of sprat above the threshold of ~18 × 1010 ind. decouple herring growth from hydro-climatic factors (i.e. salinity), and become the main driver of herring growth variations. At high sprat densities, herring growth is considerably lower than at low sprat levels, regardless of the salinity conditions, indicative of hysteresis in the response of herring growth to salinity changes. The threshold dynamic accurately explains the changes in herring growth during the past 3 decades and in turn contributes to elucidate the parallel drastic drop in herring spawning stock biomass. Studying the interplay between different stressors can provide fundamental information for the management of exploited resources. The management of the central Baltic herring stock should be adaptive and take into consideration the dual response of herring growth to hydro-climatic forces and food-web structure for a sound ecosystem approach to fisheries.

Description: Biological dinitrogen (N2) fixation is the primary input of fixed nitrogen (N) into the marine biosphere, making it an essential process contributing to the biological functions of all organisms. Because biologically available N often limits marine productivity, microbial processes leading to its loss and gain (e.g. denitrification and N2 fixation, respectively) play an important role in global biogeochemical cycles. Bioturbation is known to influence benthic N cycling, most often reported as enhancement of denitrification and a subsequent loss of N2 from the system. N2 fixation has rarely been addressed in bioturbation studies. Instead, sedimentary N2 fixation typically has been considered important in relatively rare, localized habitats such as rhizosphere and phototrophic microbial mat environments. However, the potential for N2 fixation in marine sediments may be more widespread. We show here that nitrogenase activity can be very high (up to 5 nmol C2H4 cm–3 h–1) in coastal sediments bioturbated by the ghost shrimp Neotrypaea californiensis and at depths below 5 cm. Integrated subsurface N2-fixation rates were greater than those previously found for un-vegetated estuarine sediments and were comparable to rates from photosynthetic microbial mats and rhizospheres. Inhibition experiments and genetic analysis showed that this activity was mainly linked to sulfate reduction. Sulfate-reducing bacteria (SRB) are widespread and abundant in marine sediments, with many possessing the genetic capacity to fix N2. Our results show that N2 fixation by SRB in bioturbated sediments may be an important process leading to new N input into marine sediments. Given the ubiquity of bioturbation and of SRB in marine sediments, this overlooked benthic N2 fixation may play an important role in marine N and carbon (C) cycles.

Description: To reconstruct the history of water mass exchange between the NE Atlantic and the Nordic seas, sediment cores from ∼2 km water depth were studied across Termination II (TII) and through the last interglaciation (MIS5e). During early TII the sudden appearance of the low-latitude planktonic foraminifera Beella megastoma is noted in both regions along with a steep decrease in benthic foraminiferal δ18O. Since other proxies indicate that surface waters were cold and stratified because of meltwater, conditions which prevented near-surface thermohaline circulation and vertical convection in the Nordic seas, water mass exchange between the two areas occurred at the subsurface. During later TII, surface conditions changed, and this subsurface circulation style was eventually replaced by vertical convection. In the Nordic seas, B. megastoma vanished from the record together with ice-rafted debris (IRD) at the end of TII, while subpolar foraminiferal abundance rose. Peak interglacial conditions with intensive vertical convection now fully developed, generating a bottom water temperature gradient of ∼4°C between the two areas. However, surface water temperatures deteriorated in the Nordic seas already notably before IRD recurred, and δ18O increased at the end of MIS5e.

Description: This chapter contains sections titled: Introduction Temperature Data Temperature Observations Stratospheric Water Vapor Summary and Discussion Appendix A: Linear Regression Analysis

Description: We examined the simultaneous effect of climate warming and light availability on the phytoplankton spring bloom using 1400 l (1 m depth) indoor mesocosms. The timing of the spring bloom was advanced both by warming and higher light intensity, but the influence of temperature on the phytoplankton community was stronger than the light effect. Warming affected phytoplankton directly and indirectly via enhanced grazing pressure at higher temperatures. Warming resulted in markedly lower phytoplankton biomass and a shift towards smaller cell sizes. It also led to changes in the community structure of phytoplankton and zooplankton. Among phytoplankton, large-celled diatoms were most negatively affected by warming. Overwintering zooplankton species (Oithona, Pseudocalanus) remained dominant in the cold treatments, while they were replaced by late spring or summer species (Acartia, Centropages, Temora) in the warmed treatments. Our results show that understanding food web interactions might be very important to the study of the effects of climate warming on pelagic ecosystems.

Description: Archean cratons belong to the most remarkable features of our planet since they represent continental crust that has avoided reworking for several billions of years. Even more, it has become evident from both geophysical and petrological studies that cratons exhibit deep lithospheric keels which equally remained stable ever since the formation of the cratons in the Archean. Dating of inclusions in diamonds from kimberlite pipes gives Archean ages, suggesting that the Archean lithosphere must have been cold soon after its formation in the Archean (in order to allow for the existence of diamonds) and must have stayed in that state ever since. Yet, although strong evidence for the thermal stability of Archean cratonic lithosphere for billions of years is provided by diamond dating, the long-term thermal stability of cratonic keels was questioned on the basis of numerical modeling results. We devised a viscoelastic mantle convection model for exploring cratonic stability in the stagnant lid regime. Our modeling results indicate that within the limitations of the stagnant lid approach, the application of a sufficiently high temperature-dependent viscosity ratio can provide for thermal craton stability for billions of years. The comparison between simulations with viscous and viscoelastic rheology indicates no significant influence of elasticity on craton stability. Yet, a viscoelastic rheology provides a physical transition from viscously to elastically dominated regimes within the keel, thus rendering introduction of arbitrary viscosity cutoffs, as employed in viscous models, unnecessary.

Description: A 1.6 km riser borehole was drilled at site C0009 of the NanTroSEIZE, in the center of the Kumano forearc basin, as a landward extension of previous drilling in the southwest Japan Nankai subduction zone. We determined principal horizontal stress orientations from analyses of borehole breakouts and drilling-induced tensile fractures by using wireline logging formation microresistivity images and caliper data. The maximum horizontal stress orientation at C0009 is approximately parallel to the convergence vector between the Philippine Sea plate and Japan, showing a slight difference with the stress orientation which is perpendicular to the plate boundary at previous NanTroSEIZE sites C0001, C0004 and C0006 but orthogonal to the stress orientation at site C0002, which is also in the Kumano forearc basin. These data show that horizontal stress orientations are not uniform in the forearc basin within the surveyed depth range and suggest that oblique plate motion is being partitioned into strike-slip and thrusting. In addition, the stress orientations at site C0009 rotate clockwise from basin sediments into the underlying accretionary prism.

Description: The Indian Ocean water that ends up in the Atlantic Ocean detaches from the Agulhas Current retroflection predominantly in the form of Agulhas rings and cyclones. Using numerical Lagrangian float trajectories in a high-resolution numerical ocean model, the fate of coherent structures near the Agulhas Current retroflection is investigated. It is shown that within the Agulhas Current, upstream of the retroflection, the spatial distributions of floats ending in the Atlantic Ocean and floats ending in the Indian Ocean are to a large extent similar. This indicates that Agulhas leakage occurs mostly through the detachment of Agulhas rings. After the floats detach from the Agulhas Current, the ambient water quickly looses its relative vorticity. The Agulhas rings thus seem to decay and loose much of their water in the Cape Basin. A cluster analysis reveals that most water in the Agulhas Current is within clusters of 180 km in diameter. Halfway in the Cape Basin there is an increase in the number of larger clusters with low relative vorticity, which carry the bulk of the Agulhas leakage transport through the Cape Basin. This upward cascade with respect to the length scales of the leakage, in combination with a power law decay of the magnitude of relative vorticity, might be an indication that the decay of Agulhas rings is somewhat comparable to the decay of two-dimensional turbulence.

Description: Interannual anomalies in vertical profiles of stratospheric ozone, in both equatorial and extratropical regions, have been shown to exhibit a strong seasonal persistence, namely, extended temporal autocorrelations during certain times of the calendar year. Here we investigate the relationship between this seasonal persistence of equatorial and extratropical ozone anomalies using the SAGE-corrected SBUV data set, which provides a long-term ozone profile time series. For the regions of the stratosphere where ozone is under purely dynamical or purely photochemical control, the seasonal persistence of equatorial and extratropical ozone anomalies arises from distinct mechanisms but preserves an anticorrelation between tropical and extratropical anomalies established during the winter period. In the 16–10 hPa layer, where ozone is controlled by both dynamical and photochemical processes, equatorial ozone anomalies exhibit a completely different behavior compared to ozone anomalies above and below in terms of variability, seasonal persistence, and especially the relationship between equatorial and extratropical ozone. Cross-latitude-time correlations show that for the 16–10 hPa layer, Northern Hemisphere (NH) extratropical ozone anomalies show the same variability as equatorial ozone anomalies but lagged by 3–6 months. High correlation coefficients are observed during the time frame of seasonal persistence of ozone anomalies, which is June–December for equatorial ozone and shifts by approximately 3–6 months when going from the equatorial region to NH extratropics. Thus in the transition zone between dynamical and photochemical control, equatorial ozone anomalies established in boreal summer/autumn are mirrored by NH extratropical ozone anomalies with a time lag similar to transport time scales. Equatorial ozone anomalies established in boreal winter/spring are likewise correlated with ozone anomalies in the Southern Hemisphere extratropics with a time lag comparable to transport time scales, similar to what is seen in the NH. However, the correlations between equatorial and SH extratropical ozone in the 10–16 hPa layer are weak.

Description: The linear relation between the strength of the Agulhas Current at nominal latitude 34°S and the gradient in sea level height anomaly across the current is investigated in a 1/10° resolution regional numerical ocean model. Our results show that the strength of the current can be estimated with reasonable accuracy using altimeter data, once it has been calibrated using in-situ transport measurements. Three years of transport measurements provide a calibration with worst-case correlation R = 0.78. In that case the errors in proxy transport have a standard deviation of 9.8 Sv, compared to a 20.2 Sv standard deviation of the transport time series itself. From these results we conclude that the design of the Agulhas Current Timeseries (ACT) experiment, a three-year deployment of moorings across the Agulhas Current and along a TOPEX/Jason altimeter ground track, will likely produce a good quality multi-decadal time series of Agulhas Current strength.

Description: The Ka band radar imaging mechanism of the submerged wreck/sand ribbon of the motor vessel (M/V) Birkenfels in the southern North Sea is investigated by applying the quasi‐specular scattering theory and considering the capillary as well as the gravity wave ranges of the wave energy density spectrum. For the imaging of wrecks and other oceanographic and meteorological phenomena at the sea surface it is assumed that quasi‐specular scattering becomes dominant at higher radar frequencies like Ka and X band and wind speeds ≥ 7–8 m s−1. Multibeam echo sounder images of the Birkenfels wreck and associated sand ribbons as well as other available environmental in situ data have been analyzed. The formation of sand ribbons at the sea bed and the manifestation of its radar signatures at the water surface are caused by an elliptical vortex or helical flow cell triggered by unidirectional tidal current flow interacting with the wreck. The difference between simulated and measured normalized radar cross section (NRCS) modulation as a function of the space variable is less than 31.6%. Results are presented for NRCS simulations dependent on position for different effective incidence angles, unidirectional current speeds, wind speeds, and relaxation rates. The calculated current gradient or strain rate of the imaging theory has the same order of magnitude as those obtained for marine sand waves. This implies that the responsible hydrodynamic interaction mechanism is able to produce radar signatures of submerged wrecks/sand ribbons and make them visible at the sea surface.

Description: Biological dinitrogen (N2) fixation is the primary input of fixed nitrogen (N) into the marine biosphere, making it an essential process contributing to the biological functions of all organisms. Because biologically available N often limits marine productivity, microbial processes leading to its loss and gain (e.g. denitrification and N2 fixation, respectively) play an important role in global biogeochemical cycles. Bioturbation is known to influence benthic N cycling, most often reported as enhancement of denitrification and a subsequent loss of N2 from the system. N2 fixation has rarely been addressed in bioturbation studies. Instead, sedimentary N2 fixation typically has been considered important in relatively rare, localized habitats such as rhizosphere and phototrophic microbial mat environments. However, the potential for N2 fixation in marine sediments may be more widespread. We show here that nitrogenase activity can be very high (up to 5 nmol C2H4 cm–3 h–1) in coastal sediments bioturbated by the ghost shrimp Neotrypaea californiensis and at depths below 5 cm. Integrated subsurface N2-fixation rates were greater than those previously found for un-vegetated estuarine sediments and were comparable to rates from photosynthetic microbial mats and rhizospheres. Inhibition experiments and genetic analysis showed that this activity was mainly linked to sulfate reduction. Sulfatereducing bacteria (SRB) are widespread and abundant in marine sediments, with many possessing the genetic capacity to fix N2. Our results show that N2 fixation by SRB in bioturbated sediments may be an important process leading to new N input into marine sediments. Given the ubiquity of bioturbation and of SRB in marine sediments, this overlooked benthic N2 fixation may play an important role in marine N and carbon (C) cycles.

Description: Using a global ocean model with regionally focused high resolution (1/10°) in the East China Sea (ECS), we studied the oceanic heat budget in the ECS. The modeled sea surface height variability and eddy kinetic energy are consistent with those derived from satellite altimetry. Significant levels of eddy kinetic energy are found east of the Ryukyu Islands and east of Taiwan, where the short-term variability is spawned by active mesoscale eddies coalescing with the circulation. Furthermore, the simulated vertical cross-stream structure of the Kuroshio (along the Pollution Nagasaki line) and the volume transport through each channel in the ECS are in good agreement with the observational estimates. The time-averaged temperature fluxes across the Taiwan Strait (TWS), Tsushima Strait (TSS), and the 200 m isobath between Taiwan and Japan are 0.20 PW, 0.21 PW, and 0.05 PW, respectively. The residual heat flux of 0.04 PW into the ECS is balanced by the surface heat loss. The eddy temperature flux across the 200 m isobath is 0.005 PW, which accounts for 11.2% of the total temperature flux. The Kuroshio onshore temperature flux has two major sources: the Kuroshio intrusion northeast of Taiwan and southwest of Kyushu. The Ekman temperature flux induced by the wind stress in the ECS shows the same seasonal cycle and amplitude as the onshore temperature flux, with a maximum in autumn and a minimum in summer. We conclude that the Ekman temperature flux dominates the seasonal cycle of Kuroshio onshore flux.

Description: At the Costa Rica margin along the Middle America Trench along‐strike variations in heat flow are well mapped. These variations can be understood in terms of either ventilated fluid flow, where exposed basement allows fluids to freely advect heat between the crustal aquifer and ocean, or insulated fluid flow where continuous sediment cover restricts heat advection to within the crustal aquifer. We model fluid flow within the subducting aquifer using Nusselt number approximations coupled with finite element models of subduction and explore its effect on temperatures along the subduction thrust. The sensitivity of these models to the initial thermal state of the plate and styles of fluid flow, either ventilated or insulated, is explored. Heat flow measurements on cool crust accreted at the East Pacific Rise are consistent with ventilated hydrothermal cooling that continues with subduction. These models yield much cooler temperatures than predicted from simulations initialized with conductive predictions and without hydrothermal circulation. Heat flow transects on warm crust accreted at the Cocos‐Nazca spreading center are consistent with models of insulated hydrothermal circulation that advects heat updip within the subducting crustal aquifer. Near the trench these models are warmer than conductive predictions and cooler than conductive predictions downdip of the trench. Comparisons between microseismicity and modeled isotherms suggest that the updip limit of microseismicity occurs at temperatures warmer than 100°C and that the downdip extent of microseismicity is bounded by the intersection of the subduction thrust with the base of the overriding crust.

Description: The thermal structure of convergent margins provides information related to the tectonics, geodynamics, metamorphism, and fluid flow of active plate boundaries. We report 176 heat flow measurements made with a violin bow style probe across the Costa Rican margin at the Middle America Trench. The probe measurements are collocated with seismic reflection lines. These seismic reflection lines show widespread distribution of bottom‐simulating reflectors (BSRs). To extend the spatial coverage of heat flow measurements we estimate heat flow from the depth of BSRs. Comparisons between probe measurements and BSR‐derived estimates of heat flow are generally within 10% and improve with distance landward of the deformation front. Together, these determinations provide new information on the thermal regime of this margin. Consistent with previous studies, the margin associated with the northern Nicoya Peninsula is remarkably cool. We define better the southern boundary of the cool region. The northern extent of the cool region remains poorly determined. A regional trend of decreasing heat flow landward of the deformation front is apparent, consistent with the downward advection of heat by the subducting Cocos Plate. High wave number variability at a scale of 5–10 km is significantly greater than the measurement uncertainty and is greater south of the northern Nicoya Peninsula. These heat flow anomalies vary between approximately 20 and 60 mW m−2 and are most likely due to localized fluid flow through mounds and faults on the margin. Simple one‐dimensional models show that these anomalies are consistent with flow rates of 7–15 mm yr−1. Across the margin toe variability is significant and likely due to fluid flow through deformation structures associated with the frontal sedimentary prism.

Description: A system for the shipboard measurement of air-sea CO2 fluxes by eddy covariance was developed and tested. The system was designed to reduce two major sources of experimental uncertainty previously reported. First, the correction for in situ water vapor fluctuations (the “Webb” correction) was reduced by 97% by drying the air sample stream. Second, motion sensitivity of the gas analyzer was reduced by using an open-path type sensor that was converted to a closed-path configuration to facilitate drying of the air stream. High-quality CO2 fluxes were obtained during 429 14 min flux intervals during two cruises in the North Atlantic. The results suggest that the gas analyzer resolved atmospheric CO2 fluctuations well below its RMS noise level. This noise was uncorrelated with the vertical wind and therefore filtered out by the flux calculation. Using climatological data, we estimate that the techniques reported here could enable high-quality measurements of air-sea CO2 flux over much of the world oceans.

Description: We examined the RNA and DNA concentration of field-caught scallops Chlamys islandica, maintained in suspended cultures at 15 and 30 m depth, and scallops from a wild population at 50 to 60 m in Kobbefjord, southwest Greenland. General relations between RNA and DNA concentrations and individual shell height were established, and we found that the RNA:DNA ratio (RD) worked well as a standardisation of the RNA concentration independent of size and sex. During an experimental period of 14 mo, we observed a pronounced seasonal pattern in RD and mass growth, and differences between depths. Even though the period with high levels of RD reflected the growth season relatively well, RD was a poor predictor of individual mass growth rates of C. islandica. However, we found a non-linear response in RD to increased food concentrations resulting in RD being up- and down-regulated at the beginning and end of the productive summer season, respectively. These results indicate that short-term dynamics in the actual mass growth rate might be controlled through regulation of ribosome activity rather than ribosome number (RNA concentration). This adaption would allow scallops to up-regulate protein synthesis more rapidly, thereby ensuring efficient utilisation of the intense peaks in food availability in coastal areas in the Arctic. Therefore, we suggest that RD in C. islandica reflects the growth potential rather than the actual growth rate. Still, the amount of unexplained variance in RD is considerable and not independent over time, suggesting the existence of unresolved mechanisms or relationships.

Description: Pacific Decadal Variability (PDV) and Atlantic Multidecadal Variability (AMV), the two leading decadal modes of observed Northern Hemisphere sea surface temperature (SST) variability, are investigated in a multi-millennial control integration of the Kiel Climate Model (KCM). It is shown that the two phenomena are independent modes in the model and can be easily separated by Principal Oscillation Pattern (POP) analysis of model SST. PDVrelated variability covers the whole North Pacific with strong signals in both the mid-latitude North Pacific and the western Tropical Pacific. Strong signals are also simulated in the eastern Indian Ocean Sector. PDV’s memory, however, resides in the North Pacific and is linked to the subtropical gyre. The AMV mechanism is related to the Atlantic Meridional Overturning Circulation (AMOC). A stochastic mechanism applies to both PDV and AMV.

Description: We present a new nitrogen isotope model incorporated into the three-dimensional ocean component of a global Earth system climate model designed for millennial timescale simulations. The model includes prognostic tracers for the two stable nitrogen isotopes, 14N and 15N, in the nitrate (NO3−), phytoplankton, zooplankton, and detritus variables of the marine ecosystem model. The isotope effects of algal NO3− uptake, nitrogen fixation, water column denitrification, and zooplankton excretion are considered as well as the removal of NO3− by sedimentary denitrification. A global database of δ15NO3− observations is compiled from previous studies and compared to the model results on a regional basis where sufficient observations exist. The model is able to qualitatively and quantitatively reproduce many of the observed patterns such as high subsurface values in water column denitrification zones and the meridional and vertical gradients in the Southern Ocean. The observed pronounced subsurface minimum in the Atlantic is underestimated by the model presumably owing to too little simulated nitrogen fixation there. Sensitivity experiments reveal that algal NO3− uptake, nitrogen fixation, and water column denitrification have the strongest effects on the simulated distribution of nitrogen isotopes, whereas the effect from zooplankton excretion is weaker. Both water column and sedimentary denitrification also have important indirect effects on the nitrogen isotope distribution by reducing the fixed nitrogen inventory, which creates an ecological niche for nitrogen fixers and, thus, stimulates additional N2 fixation in the model. Important model deficiencies are identified, and strategies for future improvement and possibilities for model application are outlined.

Description: [1] In the paper “A model study of the vertically integrated transport variability through the Yucatan Channel: Role of Loop Current evolution and flow compensation around Cuba” by Lin et al. (Journal of Geophysical Research, 114, C08003, doi:10.1029/2008JC005199, 2009), in the last sentence of paragraph 31, the word “westward” in “drives enhanced westward” should be “eastward.”

Description: We report total dissolved inorganic carbon (DIC) abundances and isotope ratios, as well as helium isotope ratios (3He/4He), of cold seep fluids sampled at the Costa Rica fore arc in order to evaluate the extent of carbon loss from the submarine segment of the Central America convergent margin. Seep fluids were collected over a 12 month period at Mound 11, Mound 12, and Jaco Scar using copper tubing attached to submarine flux meters operating in continuous pumping mode. The fluids show minimum 3He/4He ratios of 1.3 RA (where RA is air 3He/4He), consistent with a small but discernable contribution of mantle-derived helium. At Mound 11, δ13C∑CO2 values between −23.9‰ and −11.6‰ indicate that DIC is predominantly derived from deep methanogenesis and is carried to the surface by fluids derived from sediments of the subducting slab. In contrast, at Mound 12, most of the ascending dissolved methane is oxidized due to lower flow rates, giving extremely low δ13C∑CO2 values ranging from −68.2‰ to −60.3‰. We estimate that the carbon flux (CO2 plus methane) through submarine fluid venting at the outer fore arc is 8.0 × 105 g C km−1 yr−1, which is virtually negligible compared to the total sedimentary carbon input to the margin and the output at the volcanic front. Unless there is a significant but hitherto unidentified carbon flux at the inner fore arc, the implication is that most of the carbon being subducted in Costa Rica must be transferred to the (deeper) mantle, i.e., beyond the depth of arc magma generation.

Description: Out-of-sequence thrusts (OOST) are those thrusts which do not obey the foreland propagating or in-sequence deformation style. They include both isolated thrusts which develop hindward of the thrust front and sequences of break-back thrusts which propagate from the foreland to the hinterland. Two end-members of a series of OOST types are recognized: (1) older in-sequence thrusts which are reactivated along their entire length and (2) completely new thrusts which propagate through already deformed thrust sheets. Between the two end-members are thrusts composed partially of reactivated in-sequence thrust sequences and partially of new, entirely out-of-sequence segments. OOSTs can be initiated for a variety of reasons including: (1) keeping the orogenic wedge at critical taper, (2) break-back sequences from the suture zone in the overriding plate, (3) ramping to overcome a sticking point which inhibits in-sequence thrust propagation, and (4) during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust. Many different types of thrust behavior including gravity sliding, plucking, and derivation of isolated horses from ramps may mimic some of the characteristics of OOSTs. Consequently, it may be difficult to conclusively prove an OOST origin for a complex thrust geometry.

Description: High-resolution planktonic and epibenthic stable isotope records from Ocean Drilling Program site 658 off northwest Africa provide a basis for a detailed study of glacial terminations I-VI during the last 650,000 years. The duration of the terminations was about one half to one quarter of an orbital precession cycle (5800–10,700 years), when its amplitude was high. At low amplitudes, the terminations lasted longer than half an obliquity cycle (29,000 years). Marked climatic rebounds similar to the Younger Dryas, each with a duration of 1000–2500 years, subdivided all six terminations into distinct steps A, B, and C. Important parts of the deglacial steps were as brief as 700–1000 years. The speed of climatic change suggests that special associations existed between orbital forcing and inherent instability of the ice sheets. In harmony with published models, the more rapid pulses of glacial meltwater incursions to the northern North Atlantic led to one or more brief short-term shut-downs of North Atlantic Deep Water formation. This process is reflected by pronounced benthic δ13C minima that precisely coincide, in most cases, with the end of the δ18O deglaciation steps and immediately terminate with succeeding Younger Dryas-style cooling events. Thus we conclude that the rebounds resulted from a short-term antecedent estuarine circulation regime in the North Atlantic, except for the Younger Dryas itself, which succeeded the Alleröd with its well ventilated Atlantic deepwater circulation and hence continues to be an enigma.

Description: Analysis of the variability of equatorial ozone profiles in the Satellite Aerosol and Gas Experiment-corrected Solar Backscatter Ultraviolet data set demonstrates a strong seasonal persistence of interannual ozone anomalies, revealing a seasonal dependence to equatorial ozone variability. In the lower stratosphere (40–25 hPa) and in the upper stratosphere (6–4 hPa), ozone anomalies persist from approximately November until June of the following year, while ozone anomalies in the layer between 16 and 10 hPa persist from June to December. Analysis of zonal wind fields in the lower stratosphere and temperature fields in the upper stratosphere reveals a similar seasonal persistence of the zonal wind and temperature anomalies associated with the quasi-biennial oscillation (QBO). Thus, the persistence of interannual ozone anomalies in the lower and upper equatorial stratosphere, which are mainly associated with the well-known QBO ozone signal through the QBO-induced meridional circulation, is related to a newly identified seasonal persistence of the QBO itself. The upper stratospheric QBO ozone signal is argued to arise from a combination of QBO-induced temperature and NOx perturbations, with the former dominating at 5 hPa and the latter at 10 hPa. Ozone anomalies in the transition zone between dynamical and photochemical control of ozone (16–10 hPa) are less influenced by the QBO signal and show a quite different seasonal persistence compared to the regions above and below.

Description: Upwelling velocities w in the equatorial band are too small to be directly observed. Here, we apply a recently proposed indirect method, using the observed helium isotope (3He or 4He) disequilibria in the mixed layer. The helium data were sampled from three cruises in the eastern tropical Atlantic in September 2005 and June/July 2006. A one-dimensional two-box model was applied, where the helium air-sea gas exchange is balanced by upwelling from 3He-rich water below the mixed layer and by vertical mixing. The mixing coefficients Kv were estimated from microstructure measurements, and on two of the cruises, Kv exceeded 1 × 10−4 m2/s, making the vertical mixing term of the same order of magnitude as the gas exchange and the upwelling term. In total, helium disequilibrium was observed on 54 stations. Of the calculated upwelling velocities, 48% were smaller than 1.0 × 10−5 m/s, 19% were between 1.0 and 2.0 × 10−5 m/s, 22% were between 2.0 and 4.0 × 10−5 m/s, and on 11% of upwelling velocities exceeded this limit. The highest upwelling velocities were found in late June 2006. Meridional upwelling distribution indicated an equatorial asymmetry with higher vertical velocities between the equator and 1° to 2° south compared to north of the equator, particularly at 10°W. Associated heat flux into the mixed layer could be as high as 138 W/m2, but this depends strongly on the chosen depths where the upwelled water comes from. By combining upwelling velocities with sea surface temperature and productivity distributions, a mean monthly equatorial upwelling rate of 19 Sv was estimated for June 2006 and a biweekly mean of 24 Sv was estimated for September 2005.

Description: We estimated the air-sea gas transfer velocity for oxygen using three consecutive years (Sept. 2003 to Aug. 2006) of high-quality oxygen measurements from profiling floats in the central Labrador Sea. Mixed layer oxygen concentrations exhibit strong seasonality characterized by biologically and thermally driven evasion during spring/summer and invasion during fall/winter caused by cooling and ventilation of oxygen-deficient subsurface waters. Mixed layer oxygen budgets entirely excluding the spring bloom period are employed to estimate the air-sea transfer velocity for oxygen. By using co-located wind speed data acquired by scatterometry from the QuikSCAT satellite, wind speed dependent parameterizations for the air-sea gas transfer velocity k660 (CO2 at 20◦C and salinity 35) are established and compared with prominent parameterizations from the literature. Quadratic, cubic and quartic functions are fitted to the data for short-term and long-term wind speed averages separately. In both cases the quadratic functions yield the poorest fit to the observations. Overall, the stronger curvature of the cubic functions provides the best fit, while the quartic function also fits the data less well. Our results generally confirm the stronger wind speed dependencies among the suite of published parameterizations. Also the better fits found for cubic function points at the strong importance of very high wind speed for airsea gas exchange of O2.

Description: The Bering Sea is one of the most productive marine ecosystems in the world, sustaining nearly half of U.S. annual commercial fish catches and providing food and cultural value to thousands of coastal and island residents. Fish and crab are abundant in the Bering Sea; whales, seals, and seabirds migrate there every year. In winter, the topography, latitude, atmosphere, and ocean circulation combine to produce a sea ice advance in the Bering Sea unmatched elsewhere in the Northern Hemisphere, and in spring the retreating ice; longer daylight hours; and nutrient-rich, deep-ocean waters forced up onto the broad continental shelf result in intense marine productivity (Figure 1). This seasonal ice cover is a major driver of Bering Sea ecology, making this ecosystem particularly sensitive to changes in climate. Predicted changes in ice cover in the coming decades have intensified concern about the future of this economically and culturally important region. In response, the North Pacific Research Board (NPRB) and the U.S. National Science Foundation (NSF) entered into a partnership in 2007 to support the Bering Sea Project, a comprehensive $52 million investigation to understand how climate change is affecting the Bering Sea ecosystem, ranging from lower trophic levels (e.g., plankton) to fish, seabirds, marine mammals, and, ultimately, humans. The project integrates two research programs, the NSF Bering Ecosystem Study (BEST) and the NPRB Bering Sea Integrated Ecosystem Research Program (BSIERP), with substantial in-kind contributions from the U.S. National Oceanic and Atmospheric Administration (NOAA) and the U.S. Fish and Wildlife Service.

Description: Arctic in Rapid Transition (ART) Initiation Workshop; Fairbanks, Alaska, 7–9 November 2009; The Arctic is undergoing rapid environmental and economic transformations. Recent climate warming, which is simplifying access to oil and gas resources, enabling trans-Arctic shipping, and shifting the distribution of harvestable resources, has brought the Arctic Ocean to the top of national and international political agendas. Scientific knowledge of the present status of the Arctic Ocean and a process-based understanding of the mechanisms of change are required to make useful predictions of future conditions throughout the Arctic region. A step toward improving scientists' capacity to predict future Arctic change was undertaken with the Second International Conference on Arctic Research Planning (ICARP II) meeting in 2005 (http://web.arcticportal.org/iasc/icarp). As the ICARP II process came to a close, the Arctic in Rapid Transition (ART) initiative developed out of an effort to synthesize the several ICARP II science plans specific to the Arctic marine environment.

Description: Long-term observations show that fish and plankton populations in the ocean fluctuate in synchrony with large-scale climate patterns, but similar evidence is lacking for estuaries because of shorter observational records. Marine fish and invertebrates have been sampled in San Francisco Bay since 1980 and exhibit large, unexplained population changes including record-high abundances of common species after 1999. Our analysis shows that populations of demersal fish, crabs and shrimp covary with the Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO), both of which reversed signs in 1999. A time series model forced by the atmospheric driver of NPGO accounts for two-thirds of the variability in the first principal component of species abundances, and generalized linear models forced by PDO and NPGO account for most of the annual variability of individual species. We infer that synchronous shifts in climate patterns and community variability in San Francisco Bay are related to changes in oceanic wind forcing that modify coastal currents, upwelling intensity, surface temperature, and their influence on recruitment of marine species that utilize estuaries as nursery habitat. Ecological forecasts of estuarine responses to climate change must therefore consider how altered patterns of atmospheric forcing across ocean basins influence coastal oceanography as well as watershed hydrology.

Description: Five sediment cores from cold seeps at the forearc off Costa Rica were used to explore the relationship between fluid advection, dissolved Ca concentrations in upward migrating fluids, and authigenic CaCO3 precipitation. A numerical transport-reaction model was used to determine rates of anaerobic oxidation of methane (AOM), CaCO3 precipitation, and benthic fluxes of solutes. Production of carbonate alkalinity and formation of authigenic carbonates is most intense at intermediate flow rates (3–40 cm a−1) and reduced under low and high flux conditions (0.1 and 200 cm a−1). Dissolved Ca concentrations observed in the vent fluids off Costa Rica cover a wide range between 4 and 31 mM, clearly exceeding seawater concentrations at two locations. Systematic model runs showed that high Ca concentrations in ascending fluids enhance the rate of authigenic carbonate production at moderate flow rates leading to an almost quantitative fixation of deeply derived Ca in authigenic carbonates. Hence, CaCO3 precipitation is not only controlled by Ca diffusing into the sediment from bottom water, but also by the Ca concentration in ascending fluids. Thus, Ca enriched fluids offer a reason for enhanced subsurface CaCO3 precipitation and the occurrence of carbonate caps on dewatering structures in the Central American fore-arc. Based on average precipitation rates deduced from the systematic model runs it is possible to give a rough estimate of the global Ca-fixation at cold seeps (∼2·1010 mol Ca a−1), which suggests that cold seeps are most likely not of key importance with respect to Ca cycling in the ocean.

Description: Extremely large volcanic eruptions have been linked to global climate change, biotic turnover, and, for the Younger Toba Tuff (YTT) eruption 74,000 years ago, near-extinction of modern humans. One of the largest uncertainties of the climate effects involves evolution and growth of aerosol particles. A huge atmospheric concentration of sulfate causes higher collision rates, larger particle sizes, and rapid fall out, which in turn greatly affects radiative feedbacks. We address this key process by incorporating the effects of aerosol microphysical processes into an Earth System Model. The temperature response is shorter (9–10 years) and three times weaker (−3.5 K at maximum globally) than estimated before, although cooling could still have reached −12 K in some midlatitude continental regions after one year. The smaller response, plus its geographic patchiness, suggests that most biota may have escaped threshold extinction pressures from the eruption.

Description: Phototrophic bacteria are important primary producers of salt lakes in the Salar de Atacama and at times form visible mass developments within and on top of the lake sediments. The communities of phototrophic bacteria from two of these lakes were characterized by molecular genetic approaches using key genes for the biosynthesis of the photosynthetic apparatus in phototrophic purple bacteria (pufLM) and in green sulfur bacteria (fmoA). Terminal restriction fragment length polymorphism of the pufLM genes indicated high variability of the community composition between the two lakes and subsamples thereof. The communities were characterized by the dominance of a novel, so far undescribed lineage of pufLM containing bacteria and the presence of representatives related to known halophilic Chromatiaceae and Ectothiorhodospiraceae. In addition, the presence of BChl b-containing anoxygenic phototrophic bacteria and of aerobic anoxygenic bacteria was indicated. Green sulfur bacteria were not detected in the environmental samples, although a bacterium related to Prosthecochloris indicum was identified in an enrichment culture. This is the first comprehensive description of phototrophic bacterial communities in a salt lake of South America made possible only due to the application of the functional pufLM genes.

Description: Climate variability in the North Atlantic has been linked in part to the North Atlantic Oscillation (NAO). The NAO influences marine ecosystems in the northwestern Atlantic and transport variability of the cold Labrador Current. Understanding historic patterns of NAO variability requires long‐term and high‐resolution climate records that are not available from instrumental data. Here we present the first century‐scale proxy record of sea surface temperature (SST) variability from the Newfoundland shelf, a region from which other annual‐resolution shallow marine proxies are unavailable. The 116 year record was obtained from three sites along the eastern Newfoundland shelf using laser ablation inductively coupled mass spectrometry–determined Mg/Ca ratios in the crustose coralline alga Clathromorphum compactum. The alga is characterized by a high Mg‐calcite skeleton exhibiting annual growth increments and a century‐scale lifespan. Results indicate positive correlations between interannual variations in Mg/Ca ratios and both station‐based and gridded instrumental SST. In addition, the record shows high spatial correlations to SST across the Newfoundland shelf and the Gulf of St. Lawrence. Before 1950 the Mg/Ca proxy record reveals significant departures from gridded temperature records. While the Newfoundland shelf is generally considered a region of negative correlations to the NAO, the algal time series as well as a recent modeling study suggest a variable negative relationship with the NAO which is strongest after ∼1960 and before the mid‐1930s.

Description: Recent studies in the marine environment have suggested that the limited phenotypic plasticity of cold-adapted species like Atlantic cod (Gadus morhua L.) will cause distributions to shift toward the poles in response to rising sea temperatures. Some cod stocks are predicted to collapse, but this remains speculative because almost no information is available on the thermal tolerance of cod in its natural environment. We used electronic tags to measure the thermal experience of 384 adult Atlantic cod from eight different stocks found in the NE Atlantic. Over 100,000 days of data were collected in total. The data demonstrate that cod is an adaptable and tolerant species capable of surviving and growing in a wide range of temperate marine climates. Total thermal niche ranged from -1.5°C to 19°C; this range was narrower (1°C to 8°C) during the spawning season. Cod in each of the stocks studied had a thermal niche of approximately 12°C, but latitudinal differences in water temperature meant that cod in the warmer, southern regions experienced three times the degree days (~4000 DD year-1) than individuals from northern regions (~1200 DD year-1). Growth rates increased with temperature, reaching a maximum in those cod with a mean thermal history of between 8°C and 10°C. Our direct observations of habitat occupation suggest that adult cod will be able to tolerate warming seas but that cod populations may still be affected because the effects of marine climate change will impact cod at earlier life-history stages or via indirect effects on prey species.

Description: Based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central Chile margin (33°–46°S), we study the processes of sediment accretion and subduction and their implications on megathrust seismicity. In terms of the frontal accretionary prism (FAP) size, the marine south central Chile fore arc can be divided in two main segments: (1) the Maule segment (south of the Juan Fernández Ridge and north of the Mocha block) characterized by a relative large FAP (20–40 km wide) and (2) the Chiloé segment (south of the Mocha block and north of the Nazca-Antarctic-South America plates junction) characterized by a small FAP (≤10 km wide). In addition, the Maule and Chiloé segments correlate with a thin (〈1 km thick) and thick (∼1.5 km thick) subduction channel, respectively. The Mocha block lies between ∼37.5° and 40°S and is configured by the Chile trench, Mocha and Valdivia fracture zones. This region separates young (0–25 Ma) oceanic lithosphere in the south from old (30–35 Ma) oceanic lithosphere in the north, and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction, respectively. A process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down-deflected oceanic lithosphere under trench sediment loading. On the other hand, a small FAP along the Chiloé segment is coincident with the rupture area of the trans-Pacific tsunamigenic 1960 earthquake (Mw = 9.5), while a relatively large FAP along the Maule segment is coincident with the rupture area of the 2010 earthquake (Mw = 8.8). Differences in earthquake and tsunami magnitudes between these events can be explained in terms of the FAP size along the Chiloé and Maule segments that control the location of the updip limit of the seismogenic zone. The rupture area of the 1960 event also correlates with a thick subduction channel (Chiloé segment) that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation.

Description: This work presents data of dichlorodifluoromethane (CFC-12), dissolved inorganic carbon and total alkalinity from a cruise to the Mediterranean Sea during October–November 2001, with the main focus on the CFC-12 data and on the eastern basin. Using the transit time distribution method, the anthropogenic carbon concentrations in the basin were estimated. Results were cross-checked with a back-calculation technique. The entire water column of the Mediterranean Sea contains anthropogenic CO2, with minimum concentrations of 20.5 μmol kg−1 (error range: 16.9–27.1 μmol kg−1) in the most eastern part of the basin at intermediate depths, where the waters' mean age is 〉130 yr. Column inventories of up to 154 mol m−2 (132–179 mol m−2) are found and a total inventory of 1.7 Pg (1.3–2.1 Pg) of anthropogenic carbon in the Mediterranean Sea was estimated. There is a net flux of 38 Tg yr−1 (30–47 Tg yr−1) of dissolved inorganic carbon through the Strait of Gibraltar into the Atlantic Ocean and an opposite net flux of 3.5 Tg yr−1 (−1.8–9.2 Tg yr−1) of anthropogenic carbon into the Mediterranean Sea.

Description: Bubble transport of methane from shallow seep sites in the Black Sea west of the Crimea Peninsula between 70 and 112 m water depth has been studied by extrapolation of results gained through different hydroacoustic methods and direct sampling. Ship-based hydroacoustic echo sounders can locate bubble releasing seep sites very precisely and facilitate their correlation with geological or other features at the seafloor. Here, the backscatter strength of a multibeam system was integrated with single-beam data to estimate the amount of seeps/m2 for different backscatter intensities, resulting in 2709 vents in total. Direct flux measurements by submersible revealed methane fluxes from individual vents of 0.32–0.85 l/min or 14.5–37.8 mmol/min at ambient pressure and temperature conditions. A conservative estimate of 30 mmol/min per site was used to estimate the flux into the water to be 1219–1355 mmol/s. The flux to the atmosphere was calculated by applying a bubble dissolution model taking release depth, temperature, gas composition, and bubble size spectra into account. The flux into the atmosphere (3930–4533 mol/d) or into the mixed layer (6186–6899 mol/d) from the 21.8 km2 large study area is three times higher than independently measured fluxes of dissolved methane for the same area using geochemical methods (1030–2495 mol/d). The amount of methane dissolving in the mixed layer is 2256–2366 mol/d. This close match shows that the hydroacoustic approach for extrapolating the number of seeps/m2 and the applied bubble dissolution model are suitable to extrapolate methane fluxes over larger areas.

Description: Understanding the influence of solar variability on the Earth's climate requires knowledge of solar variability, solar-terrestrial interactions, and the mechanisms determining the response of the Earth's climate system. We provide a summary of our current understanding in each of these three areas. Observations and mechanisms for the Sun's variability are described, including solar irradiance variations on both decadal and centennial time scales and their relation to galactic cosmic rays. Corresponding observations of variations of the Earth's climate on associated time scales are described, including variations in ozone, temperatures, winds, clouds, precipitation, and regional modes of variability such as the monsoons and the North Atlantic Oscillation. A discussion of the available solar and climate proxies is provided. Mechanisms proposed to explain these climate observations are described, including the effects of variations in solar irradiance and of charged particles. Finally, the contributions of solar variations to recent observations of global climate change are discussed.

Description: We present a set of six 20 year experiments made with a state-of-the-art chemistry-climate model that incorporates the atmosphere from the surface to the lower thermosphere. The response of the middle atmosphere to the 11 year solar cycle, its impact on the troposphere, and especially the role of an externally prescribed stratospheric quasi-biennial oscillation (QBO) is investigated with NCAR's Whole Atmosphere Community Climate Model (WACCM3). The model experiments use either fixed solar cycle inputs or fixed solar cycle together with prescribed QBO phase. The annual mean solar response in temperature and ozone in the upper stratosphere is in qualitative agreement with other modeling and observational studies and does not depend on the presence of the imposed QBO. However, the solar response in the middle to lower stratosphere differs significantly for the two QBO phases. During solar maxima a weaker Brewer-Dobson circulation with relative downwelling, warming, and enhanced ozone occurs in the tropical lower stratosphere during QBO east conditions, while a stronger circulation, cooling, and decreased ozone exists during QBO west conditions. The net ozone increase during QBO east is the combined result of production and advection, whereas during QBO west the effects cancel each other and result in little net ozone changes. Especially during Southern Hemisphere late winter to early spring, the solar response at polar latitudes switches sign between the two QBO phases and qualitatively confirms observations and other recent model studies. During a poleward downward modulation of the polar night jet and a corresponding modulation of the Brewer-Dobson circulation in time, solar signals are detected all the way down to the extratropical troposphere. Possible limitations of the model experiments with respect to the fixed solar cycle conditions or the prescribed QBO phases, as well as the constant sea surface temperatures, are discussed.

Description: The distribution of dissolved methane in the water column of the Baltic Sea was extensively investigated. A strong correlation between the vertical density stratification, the distribution of oxygen, hydrogen sulfide, and methane has been identified. A widespread release of methane from the seafloor is indicated by increasing methane concentrations with water depth. The deep basins in the central Baltic Sea show the strongest methane enrichments in stagnant anoxic water bodies (max. 1086 nM and 504 nM, respectively), with a pronounced decrease towards the pelagic redoxcline and slightly elevated surface water concentrations (saturation values of 206% and 120%, respectively). In general the more limnic basins in the northern part of the Baltic are characterized by lower water column methane concentrations and surface water saturation values close to the atmospheric equilibrium (between 106% and 116%). In contrast, the shallow Western Baltic Sea is characterized by high saturation values up to 746%.

Description: The goal of the Chemistry-Climate Model Validation (CCMVal) activity is to improve understanding of chemistry-climate models (CCMs) through process-oriented evaluation and to provide reliable projections of stratospheric ozone and its impact on climate. An appreciation of the details of model formulations is essential for understanding how models respond to the changing external forcings of greenhouse gases and ozone-depleting substances, and hence for understanding the ozone and climate forecasts produced by the models participating in this activity. Here we introduce and review the models used for the second round (CCMVal-2) of this intercomparison, regarding the implementation of chemical, transport, radiative, and dynamical processes in these models. In particular, we review the advantages and problems associated with approaches used to model processes of relevance to stratospheric dynamics and chemistry. Furthermore, we state the definitions of the reference simulations performed, and describe the forcing data used in these simulations. We identify some developments in chemistry-climate modeling that make models more physically based or more comprehensive, including the introduction of an interactive ocean, online photolysis, troposphere-stratosphere chemistry, and non-orographic gravity-wave deposition as linked to tropospheric convection. The relatively new developments indicate that stratospheric CCM modeling is becoming more consistent with our physically based understanding of the atmosphere.

Description: Large-scale sea-ice thickness and surface property data were obtained in three summers and in three different sea-ice regimes in the Arctic Trans-Polar Drift (TPD) by means of helicopter electromagnetic sounding. Distribution functions P of sea-ice thickness and of the height, spacing, and density of sails were analyzed to characterize ice regimes of different ages and deformations. Results suggest that modal ice thickness is affected by the age of a sea-ice regime and that the degree of deformation is represented by the shape of P. Mean thickness changes with both age and deformation. Standard error calculations showed that representative mean and modal thickness could be obtained with transect lengths of 15 km and 50 km, respectively, in less deformed ice regimes such as those around the North Pole. In heavier deformed ice regimes closer to Greenland, 100 km transects were necessary for mean thickness determination and a representative modal thickness could not be obtained at all. Mean sail height did not differ between ice regimes, whereas sail density increased with the degree of deformation. Furthermore, the fraction of level ice, open melt ponds, and open water along the transects were determined. Although overall ice thickness in the central TPD was 50% thinner in 2007 than in 2001, first-year ice (FYI) was not significantly thinner in 2007 than FYI in 2001, with a decrease of only 0.3 m. Thinner FYI in 2007 only occurred close to the sea-ice edge, where open water covered more than 10% of the surface. Melt pond coverage retrieved from laser measurements was 15% in both the 2004 MYI regime and the 2007 FYI regime.

Description: The multidecadal variability of air-sea CO(2)fluxes in the North Atlantic under preindustrial atmospheric CO(2) conditions is simulated, using a coupled biogeochemical/circulation model driven by long-term surface forcing reconstructed from the leading modes of sea level pressure observations from 1850 to 2000. Heat fluxes are of great importance for the multidecadal CO(2) fluctuations, about equal in magnitude to wind stress, in contrast to their less prominent role for CO(2) flux variability on interannual timescales. Another difference, compared to higher frequencies, is the dominance of the North Atlantic Oscillation in driving the variability of the air-sea CO(2) fluxes. Two spatially distinct regimes lead to large anomalies in the CO(2) fluxes but compensate to a large degree. The first regime is advective and has its clear signature southeast of Greenland while the second one, in the vicinity of the Labrador Sea and off Newfoundland, is convective. In both regimes, the multidecadal CO(2) fluctuations are driven mainly by variations in temperature, salinity, and DIC content at the sea surface while the role of the biological pump is of minor importance in this particular model. The magnitude of the simulated multidecadal CO(2) uptake changes is on the order of 0.02 Pg C/yr and amounts to 10-15% of the estimated annual anthropogenic CO(2) uptake of the North Atlantic.

Description: In order to validate the reported precision of space-based atmospheric composition measurements, validation studies often focus on measurements in the tropical stratosphere, where natural variability is weak. The scatter in tropical measurements can then be used as an upper limit on single-profile measurement precision. Here we introduce a method of quantifying the scatter of tropical measurements which aims to minimize the effects of short-term atmospheric variability while maintaining large enough sample sizes that the results can be taken as representative of the full data set. We apply this technique to measurements of O(3), HNO(3), CO, H(2)O, NO, NO(2), N(2)O, CH(4), CCl(2)F(2), and CCl(3)F produced by the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS). Tropical scatter in the ACE-FTS retrievals is found to be consistent with the reported random errors (RREs) for H(2)O and CO at altitudes above 20 km, validating the RREs for these measurements. Tropical scatter in measurements of NO, NO(2), CCl(2)F(2), and CCl(3)F is roughly consistent with the RREs as long as the effect of outliers in the data set is reduced through the use of robust statistics. The scatter in measurements of O(3), HNO(3), CH(4), and N(2)O in the stratosphere, while larger than the RREs, is shown to be consistent with the variability simulated in the Canadian Middle Atmosphere Model. This result implies that, for these species, stratospheric measurement scatter is dominated by natural variability, not random error, which provides added confidence in the scientific value of single-profile measurements.

Description: Photoacclimation models are a prerequisite for accurate estimates of primary production in aquatic environments under typically variable light conditions. They generally start from empirical functions of the internal chlorophyll a (chl a) or nutrient quota (e.g. the Droop model). We propose that physiological variations in phytoplankton reflect phenotypic adaptation which maximizes the growth rate. Growth maximization has to account for indirect effects of the enhancement of carbon (C) acquisition by acclimation, primarily through concomitant changes in the intracellular nitrogen (N) budget. Our model expresses, for the first time, the indirect effect of alterations in N uptake on C assimilation by a parameter-free trade-off between the 2 uptake functions. The model explicitly prescribes optimal protein partitioning between N and C uptake and sub-partitioning into carboxylation (1,5-bisphosphate carboxylase/oxygenase, Rubisco) and light harvesting. Applications to various published experimental data for different phytoplankton species support the validity of the optimality hypothesis and point to different flexibility in the re-organization of chloroplasts between taxa as well as to different time-scales on which photoacclimation operates. Simulations of a batch culture with the haptophyte Isochrysis galbana show that a decoupling in pigment N:C from cellular N:C may explain observed lag phases in chl a:C regulation. For diatoms, seemingly stronger constraints in intra-cellular stoichiometry determine the photoacclimative response to variable light regimes, as simulated and reported for Skeletonema costatum. N and chl a quotas correlate well in nutrient-limited chemostats of Thalassiosira fluviatilis, but in part decouple under light limitation. In N limited growth, non-linearity in N:C as expressed by the Droop function results from a combination of a linear quota dependency, down-regulation of relative carboxylation capacity, and increasing N costs of chl a synthesis at elevated growth rates. Our optimality assumption that includes indirect feed-backs through the concept of protein partitioning generates an accurate model for adaptation in physiological traits.

Description: Zooplankton feeding formulations in plankton models have exclusively focused on the relation between food concentration and ingestion, with respiration and excretion being treated separately, despite experimental evidence for strong links among these processes. We present an optimal current-feeding model linking ingestion, respiration, and assimilation efficiency to foraging activity. The Ivlev model is a special case of our optimal current-feeding model, which applies to static feeding behaviour. We validate our model with experimental data for copepods, ciliates, and dinoflagellates. Parameter estimates suggest that phylogenetic grouping is more important than predator size in determining feeding behaviour. Respiratory costs of foraging, e.g. for generating a feeding current, may be much larger than previously thought, are larger in smaller organisms, and might explain the independent development of feeding thresholds in different micro- and mesozooplankton groups. Both preferential feeding on, and lower feeding thresholds for, larger food particles are predicted to derive from greater capture efficiency owing to enhanced detectability of larger particles. The relation between feeding threshold and prey size appears to depend on feeding strategy but not on predator size, as a common relationship seems to apply for current feeders (ciliates and copepods) spanning a vast size range. Our model exhibits an inverse relationship between ingestion and assimilation efficiency, reducing the contribution of copepods to export of organic matter relative to remineralisation at low food concentrations. Export ratio variations previously thought to require strong shifts in community composition can be generated by changes in feeding behaviour predicted by our model.

Description: This paper examines a hydrographic response to the wind‐driven coastal polynya activity over the southeastern Laptev Sea shelf for April–May 2008, using a combination of Environmental Satellite (Envisat) advanced synthetic aperture radar (ASAR) and TerraSAR‐X satellite imagery, aerial photography, meteorological data, and SBE‐37 salinity‐temperature‐depth and acoustic Doppler current profiler land‐fast ice edgemoored instruments. When ASAR observed the strongest end‐of‐April polynya event with frazil ice formation, the moored instruments showed maximal acoustical scattering within the surface mixed layer, and the seawater temperatures were either at or 0.02°C below freezing. We also find evidence of the persistent orizontal temperature and salinity gradients across the fast ice edge to have the signature of geostrophic flow adjustment as predicted by polynya models.

Description: Nitrous oxide (N2O) flux densities across the ocean/atmosphere interface from the Mauritanian upwelling (16°–18.5°W, 16°–21°N) were computed with a simple upwelling model using N2O measurements from four cruises between 2006 and 2008 as well as wind data from the QuikSCAT satellite. The resulting N2O flux densities show a strong seasonality reflecting the wind-driven seasonality of the upwelling: N2O flux densities are highest in the northern part (19.5°–21°N) and show a decreasing trend towards the south. The summer periods with no upwelling (and thus associated with no or negligible N2O flux densities) are most pronounced in the southern part (16°–17°N). The mean seasonally and regionally weighted annual N2O emissions from the Mauritanian upwelling were estimated to 1.0 Gg N. This is low compared to other major upwelling areas (Arabian Sea, off Chile) indicating that N2O emissions from the Mauritanian upwelling are a minor source of atmospheric N2O.

Description: Unraveling the processes responsible for Earth’s climate transition from an “El Niño–like state” during the warm early Pliocene into a modern‐like “La Niña–dominated state” currently challenges the scientific community. Recently, the Pliocene climate switch has been linked to oceanic thermocline shoaling at ∼3 million years ago along with Earth’s final transition into a bipolar icehouse world. Here we present Pliocene proxy data and climate model results, which suggest an earlier timing of the Pliocene climate switch and a different chain of forcing mechanisms. We show that the increase in North Atlantic meridional overturning circulation between 4.8 and 4.0 million years ago, initiated by the progressive closure of the Central American Seaway, triggered overall shoaling of the tropical thermocline. This preconditioned the turnaround from a warm eastern equatorial Pacific to the modern equatorial cold tongue state about 1 million years earlier than previously assumed. Since ∼3.6–3.5 million years ago, the intensification of Northern Hemisphere glaciation resulted in a strengthening of the trade winds, thereby amplifying upwelling and biogenic productivity at low latitudes.

Description: Geophysical investigations of the northern Hikurangi subduction zone northeast of New Zealand, image fore‐arc and surrounding upper lithospheric structures. A seismic velocity (Vp) field is determined from seismic wide‐angle data, and our structural interpretation is supported by multichannel seismic reflection stratigraphy and gravity and magnetic modeling. We found that the subducting Hikurangi Plateau carries about 2 km of sediments above a 2 km mixed layer of volcaniclastics, limestone, and chert. The upper plateau crust is characterized by Vp = 4.9–6.7 km/s overlying the lower crust with Vp 〉 7.1 km/s. Gravity modeling yields a plateau thickness around 10 km. The reactivated Raukumara fore‐arc basin is 〉10 km deep, deposited on 5–10 km thick Australian crust. The fore‐arc mantle of Vp 〉 8 km/s appears unaffected by subduction hydration processes. The East Cape Ridge fore‐arc high is underlain by a 3.5 km deep strongly magnetic (3.3 A/m) high‐velocity zone, interpreted as part of the onshore Matakaoa volcanic allochthon and/or uplifted Raukumara Basin basement of probable oceanic crustal origin. Beneath the trench slope, we interpret low‐seismic‐velocity, high‐attenuation, low‐density fore‐arc material as accreted and recycled, suggesting that underplating and uplift destabilizes East Cape Ridge, triggering two‐sided mass wasting. Mass balance calculations indicate that the proposed accreted and recycled material represents 25–100% of all incoming sediment, and any remainder could be accounted for through erosion of older accreted material into surrounding basins. We suggest that continental mass flux into the mantle at subduction zones may be significantly overestimated because crustal underplating beneath fore‐arc highs have not properly been accounted for.

Description: An array of broadband seismometers transecting the Talamanca Range in southern Costa Rica was operated from 2005 until 2007. In combination with data from a short‐period network near Quepos in central Costa Rica, this data is analyzed by the receiver function method to image the crustal structure in south‐central Costa Rica. Two strong positive signals are seen in the migrated images, interpreted as the Moho (at around 35 km depth) and an intra‐crustal discontinuity (15 km depth). A relatively flat crustal and Moho interface underneath the north‐east flank of the Talamanca Range can be followed for a lateral distance of about 50 km parallel to the trench, with only slight changes in the overall geometry. Closer to the coast, the topography of the discontinuities shows several features, most notably a deeper Moho underneath the Talamanca Mountain Range and volcanic arc. Under the highest part of the mountain ranges, the Moho reaches a depth of about 50 km, which indicates that the mountain ranges are approximately isostatically compensated. Local deviations from the crustal thickness expected for isostatic equilibrium occur under the active volcanic arc and in south Costa Rica. In the transition region between the active volcanic arc and the Talamanca Range, both the Moho and intracrustal discontinuity appear distorted, possibly related to the southern edge of the active volcanic zone and deformation within the southern part of the Central Costa Rica Deformed Belt. Near the volcanoes Irazu and Turrialba, a shallow converter occurs, correlating with a low‐velocity, low‐density body seen in tomography and gravimetry. Applying a grid search for the crustal interface depth and vp/vs ratio cannot constrain vp/vs values well, but points to generally low values (〈1.7) in the upper crust. This is consistent with quartz‐rich rocks forming the mountain range.

Description: Seventeen inorganic germanium and silicon concentration profiles collected from the Atlantic, southwest Pacific, and Southern oceans are presented. A plot of germanium concentration versus silicon concentration produced a near-linear line with a slope of 0.760 × 10−6 (±0.004) and an intercept of 1.27 (±0.24) pmol L−1 (r2 = 0.993, p 〈 0.001). When the germanium-to-silicon ratios (Ge/Si) were plotted versus depth and/or silicon concentrations, higher values are observed in surface waters (low in silicon) and decreased with depth (high in silicon). Germanium-to-silicon ratios in diatoms (0.608–1.03 × 10−6) and coupled seawater samples (0.471–7.46 × 10−6) collected from the Southern Ocean are also presented and show clear evidence for Ge/Si fractionation between the water and opal phases. Using a 10 box model (based on PANDORA), Ge/Si fractionation was modeled using three assumptions: (1) no fractionation, (2) fractionation using a constant distribution coefficient (KD) between the water and solid phase, and (3) fractionation simulated using Michaelis-Menten uptake kinetics for germanium and silicon via the silicon uptake system. Model runs indicated that only Ge/Si fractionation based on differences in the Michaelis-Menten uptake kinetics for germanium and silicon can adequately describe the data. The model output using this fractionation process produced a near linear line with a slope of 0.76 × 10−6 and an intercept of 0.92 (±0.28) pmol L−1, thus reflecting the oceanic data set. This result indicates that Ge/Si fractionation in the global ocean occurs as a result of subtle differences in the uptake of germanium and silicon via diatoms in surface waters.

Description: The impact of moderate environmental stress may be modulated by stress-induced shifts of biotic interactions such as host – epibiont relationships. We studied the stress regime in shallow Western Baltic habitats, the variability of fouling at different temporal and spatial scales, and whether common stressors - low light, high temperature, grazing – affect the abundance and composition of the biofilm on a regionally important macroalga, the bladder wrack Fucus vesiculosus. We further explore the alga’s capacity to chemically modulate the recruitment of microfoulers and whether this ability is impacted by stress. In laboratory, mesocosm and field experiments fouling pressure and epibiotic cover on the algae varied strongly with changing environmental conditions such as temperature, irradiance, depth or grazing. The expectation that abiotic stress affects the fouling-modulating ability of the alga and, thus, indirectly produces the observed variability of epibiosis was not generally confirmed. Indeed, while the strength of chemical antifouling resistance varied seasonally, with a maximum in winter/spring and a minimum in late summer, this could not be related to temporal patterns of environmental stress, fouling pressure, or growth of Fucus. Only the seasonal variation in reproduction seemed to be in phase with antifouling activity. Controlled experiments confirmed that resistance strength was not affected by temperature or grazing, and only moderately by light. We conclude that the fouling modulation ability of Fucus vesiculosus may suffer from light-reduction (e.g. by eutrophication effects) while they are not sensitive to the predicted warming or enhanced grazing.

Description: We review research from the last 40 yr on macroalgal–bacterial interactions. Marine macroalgae have been challenged throughout their evolution by microorganisms and have developed in a world of microbes. Therefore, it is not surprising that a complex array of interactions has evolved between macroalgae and bacteria which basically depends on chemical interactions of various kinds. Bacteria specifically associate with particular macroalgal species and even to certain parts of the algal body. Although the mechanisms of this specificity have not yet been fully elucidated, ecological functions have been demonstrated for some of the associations. Though some of the chemical response mechanisms can be clearly attributed to either the alga or to its epibiont, in many cases the producers as well as the mechanisms triggering the biosynthesis of the biologically active compounds remain ambiguous. Positive macroalgal–bacterial interactions include phytohormone production, morphogenesis of macroalgae triggered by bacterial products, specific antibiotic activities affecting epibionts and elicitation of oxidative burst mechanisms. Some bacteria are able to prevent biofouling or pathogen invasion, or extend the defense mechanisms of the macroalgae itself. Deleterious macroalgal–bacterial interactions induce or generate algal diseases. To inhibit settlement, growth and biofilm formation by bacteria, macroalgae influence bacterial metabolism and quorum sensing, and produce antibiotic compounds. There is a strong need to investigate the bacterial communities living on different coexisting macroalgae using new technologies, but also to investigate the production, localization and secretion of the biological active metabolites involved in those possible ecological interactions.

Description: The sensitivity of sea level to melting from polar ice sheets and glaciers during recent natural and anthropogenic climate fluctuations is poorly constrained beyond the period of direct observation by satellite. We have investigated glacial meltwater events during the Anthropocene by adapting the pioneering approach of modeling trends in d18O in the pore waters of deep‐sea cores, previously used to constrain the size of ice sheets during the Last Glacial Maximum. We show that during recent warm periods, meltwater from glacier retreat drains into the coastal fjords, leaving a signature of depleted d18O values and low Cl concentrations in the pore water profiles of rapidly accumulating sediments. Here we model such pore water profiles in a piston core to constrain the timing and magnitude of an ice sheet retreat event at Caley Glacier on the west Antarctic Peninsula, and the result is compared with local ice front movement. This approach of pore water modeling was then applied in another kasten core and tested by a series of sensitivity analyses. The results suggest that our approach may be applied in fjords of different sedimentary settings to reconstruct the glacier history and allow insight into the sensitivity of polar glaciers to abrupt warming events.

Description: Combined salinity and δ18O data from summer 2007 reveal a significant change in brine production in the Laptev Sea relative to summer 1994. The distribution of river water and brine enriched waters on the Laptev Sea shelf is derived based on mass balance calculations using salinity and δ18O data. While in 1994 maximal influence of brines is seen within bottom waters [Bauch et al., 2009a], in 2007 the influence of brines is highest within the surface layer and only a moderate influence of brines is observed in the bottom layer. In contrast to 2007, salinity and δ18O data from summer 1994 clearly identify a locally formed brine enriched bottom water mass as mixing endmember between surface layer and inner shelf waters on one side and with higher salinity water from the outer Laptev Sea on the other side. In 2007 the brine enriched waters are predominantly part of the surface regime and the mixing endmember between surface layer and outer shelf waters is replaced by a relatively salty bottom water mass. This relatively salty bottom water probably originates from the western Laptev Sea. The inverted distribution of brines in the water column in 2007 relative to 1994 suggests a less effective winter sea-ice formation in winter 2006/2007 combined with advection of more saline waters from the western Laptev Sea or the outer shelf precedent to 1 the climatically extreme summer 2007. The observed changes result in an altered export of waters from the Laptev Sea to the Arctic Ocean halocline.

Description: The recent overall Northern Hemisphere warming was accompanied by several severe northern continental winters, as for example, extremely cold winter 2005/2006 in Europe and northern Asia. Here we show that anomalous decrease of wintertime sea ice concentration in the Barents-Kara (B-K) Seas could bring about extreme cold events like winter 2005/2006. Our simulations with the ECHAM5 general circulation model demonstrate that lower-troposphere heating over the B-K Seas in the Eastern Arctic caused by the sea ice reduction may result in strong anti-cyclonic anomaly over the Polar Ocean and anomalous easterly advection over northern continents. This causes a continental-scale winter cooling reaching -1.5°C, with more than three times increased probability of cold winter extremes over large areas including Europe. Our results imply that several recent severe winters do not conflict the global warming picture but rather supplement it, being in qualitative agreement with the simulated large-scale atmospheric circulation realignment. Furthermore, our results suggest that high-latitude atmospheric circulation response to the B-K sea ice decrease is highly nonlinear and characterized by transition from anomalous cyclonic circulation to anticyclonic one and then again back to cyclonic type of circulation as the B-K sea ice concentration gradually reduces from 100% to ice free conditions. We present a conceptual model which may explain the nonlinear local atmospheric response in the B-K Seas region by counter play between convection over the surface heat source and baroclinic effect due to modified temperature gradients in the vicinity of the heating area.

Description: The dynamics of the Equatorial Atlantic zonal mode are studied using observed sea surface height (SSH), sea surface temperature (SST), and heat flux and reanalysis wind stress and upper ocean temperature. Principal oscillation pattern (POP) analysis shows that the zonal mode is an oscillatory normal-mode of the observed coupled system, obeying the delayed-action/recharge oscillator paradigm for ENSO. Variations in equatorial averaged SSH, a proxy for upper ocean heat content, precede SST anomalies in the cold tongue by 4-5 months, about a quarter of the POP period. Positive subsurface temperature anomalies appear in the west, as a delayed response to the preceding cold event. These propagate eastward, where due to the shallow thermocline they can influence SST, leading to the next warm event. Although SST variations exhibit weak westward propagation during some zonal mode events, POP analysis indicates that to first order there is no zonal propagation in SST. Net surface heat flux anomalies generally act to damp SST anomalies. The zonal mode explains a large amount (70%) of SST variability in the east and a significant fraction (19%) of equatorial variability. Thus, the predictability potential in the Equatorial Atlantic on seasonal time scales may be considerably higher than currently thought.

Description: Analyses of clone libraries from water and sediments of different sites from Salar de Huasco, a high-altitude athalassohaline wetland in the Chilean Altiplano, revealed the presence of five unique clusters of uncultured Archaea that have not been previously reported or specifically assigned. These sequences were distantly related (83–96% sequence identity) to a limited number of other clone sequences and revealed no identity to cultured Archaea. The abundance of Archaea and Bacteria was estimated using qPCR and community composition was examined through the construction of clone libraries of archaeal 16S rRNA gene. Archaea were found to be dominant over Bacteria in sediments from two saline sites (sites H4: 6.31 × 104 and site H6: 1.37 × 104 μS cm−1) and in one of the water samples (freshwater from site H0: 607 μS cm−1). Euryarchaeotal sequences were more abundant than crenarchaeotal sequences. Many of the clone sequences (52%) were similar to uncultured archaeal groups found in marine ecosystems having identity values between 99% and 97%. A major fraction of the sequences (40%) were members of Methanobacteria, while others were included in the Marine Benthic Groups B and D, the Miscellaneous Crenarchaeotic Group, the Terrestrial Miscellaneous Euryarchaeotal Group, Marine Group I and Halobacteria. The presence of uncultured archaeal groups in Salar de Huasco extends their known distribution in inland waters, providing new clues about their possible function in the environment.

Description: Life at deep-sea hydrothermal vents depends on chemolithoautotrophic microorganisms as primary producers mediating the transfer of energy from hydrothermal fluids to higher trophic levels. A comprehensive molecular survey was performed with microbial communities in a mussel patch at the Irina II site of the Logatchev hydrothermal field by combining the analysis of 16S rRNA gene sequences with studies of functional key genes involved in biochemical pathways of sulfur oxidation–reduction (soxB, aprA) and autotrophic carbon fixation (aclB, cbbM, cbbL). Most significantly, major groups of chemoautotrophic sulfur oxidizers in the diffuse fluids differed in their biosynthetic pathways of both carbon fixation and sulfur oxidation. One important component of the community, the Epsilonproteobacteria, has the potential to grow chemoautotrophically by means of the reductive tricarboxylic acid cycle and to gain energy through the oxidation of reduced sulfur compounds using the Sox pathway. The majority of soxB and all retrieved aclB gene sequences were assigned to this group. Another important group in this habitat, the Gammaproteobacteria, may use the adenosine 5'-phosphosulfate pathway and the Calvin–Benson–Bassham cycle, deduced from the presence of aprA and cbbM genes. Hence, two important groups of primary producers at the investigated site might use different pathways for sulfur oxidation and carbon fixation.

Description: We present an analysis of the variability of the liquid Arctic freshwater (FW) export, using a simulation from the Community Climate System Model Version 3 (CCSM3) that includes passive tracers for FW from different sources. It is shown that the FW exported through the western Canadian Arctic Archipelago (CAA) comes mainly from the Pacific and from North American runoff. The variability of the FW export from both of these sources is generally in phase, due to the strong influence of variations of the velocity anomaly on the CAA FW export variability. The velocity anomaly in the CAA is in turn mainly governed by variations in the large-scale atmospheric circulation (i.e., the Arctic Oscillation). In Fram Strait, the FW export is mainly composed of Eurasian runoff and FW of Pacific origin. The variability of the Fram Strait FW export is governed both by changes in the velocity and in the FW concentration, and the variability of the FW concentration from the two largest sources is not in phase. The Eurasian runoff export through Fram Strait depends strongly on the release of FW from the Eurasian shelf, which occurs during years with an anticyclonic circulation anomaly (negative Vorticity index) and takes 3 years to reach Fram Strait after leaving the shelf. In contrast, the variability of the Pacific FW export through Fram Strait is mainly controlled by changes in the Pacific FW storage in the Beaufort Gyre, with an increased export during years with a cyclonic circulation anomaly (positive Vorticity index).

Description: Interannual variability of tropical Pacific sea surface temperatures (SST) has an asymmetry with stronger positive events, El Niño, and weaker negative events, La Niña, which is generally attributed to processes in the ocean. Here we present evidence from a new hybrid coupled model that the asymmetry and seasonality of El Niño can be caused by nonlinear and seasonally varying atmospheric feedbacks. The model consists of the ECHAM5 global atmospheric general circulation model (GCM) coupled to the 2-dimensional El Niño linear recharge oscillator ocean model in the tropical Pacific and a mixed layer ocean elsewhere. Despite the models simplistic and, by construction, linear representation of the ocean dynamics, it is able to simulate the main statistical features of El Niño including period, seasonality, skewness, and kurtosis. Analyses of the model show that a nonlinear relationship between zonal wind stress and SST is causing the El Niño-La Niña asymmetry.

Description: The vertical distribution of methane- and ammonia-oxidizing bacteria (MOB and AOB, respectively), and the physicochemical conditions in the chemocline of Lake Kinneret (Israel) were studied at a resolution of 10 cm from 16.2 to 17.7 m depth. Profiles of the chemical parameters indicated decreasing concentrations of methane (from 22.4 to 0.11 µmol l–1) and ammonia (from 14.2 to 8.4 µmol l–1) towards the water surface and in close proximity to the chemocline. The disappearance of methane coincided with methane oxidation that could be corroborated throughout this layer with highest rates at 17.4 to 17.6 m. Disappearance of ammonia could not be linked to ammonia oxidation exclusively. The genes pmoA and the homologous amoA (coding for subunit α of the methane and ammonia monooxygenase, respectively) were amplified by PCR. The products were analyzed by terminal restriction fragment length polymorphism (T-RFLP) and sequencing of clone libraries. The results demonstrated that different MOB and AOB communities are established along the concentration gradient within the narrow layer of the metalimnetic chemocline. Changes in the intensity of the T-RFLP peaks and the frequency of different groups of alpha- and gammaproteobacterial MOB, and betaproteobacterial AOB, coincided with the concentration gradients of methane, ammonia, nitrate, and oxygen in the chemocline. This suggests that different communities of MOB, and to a lesser extent AOB, contribute to the formation of chemical gradients of their particular substrates in the chemocline

Description: The Sunda‐Banda arc transition at the eastern termination of the Sunda margin (Indonesia) represents a unique natural laboratory to study the effects of lower plate variability on upper plate deformational segmentation. Neighboring margin segments display a high degree of structural diversity of the incoming plate (transition from an oceanic to a continental lower plate, presence/absence of an oceanic plateau, variability of subducting seafloor morphology) as well as a wide range of corresponding fore‐arc structures, including a large sedimentary basin and an accretionary prism/outer arc high of variable size and shape. Here, we present results of a combined analysis of seismic wide‐angle refraction, multichannel streamer and gravity data recorded in two trench normal corridors located offshore the islands of Lombok (116°E) and Sumba (119°E). On the incoming plate, the results reveal a 8.6–9.0 km thick oceanic crust, which is progressively faulted and altered when approaching the trench, where upper mantle velocities are reduced to ∼7.5 km/s. The outer arc high, located between the trench and the fore‐arc basin, is characterized by sedimentary‐type velocities (Vp 〈 5.5 km/s) down to the top of the subducting slab (∼13 km depth). The oceanic slab can be traced over 70–100 km distance beneath the fore arc. A shallow serpentinized mantle wedge at ∼16 km depth offshore Lombok is absent offshore Sumba, where our models reveal the transition to the collisional regime farther to the east and to the Sumba block in the north. Our results allow a detailed view into the complex structure of both the deeper and shallower portions of the eastern Sunda margin.

Description: Past sea surface temperatures (SSTs) are routinely estimated from organic and inorganic remains of fossil phytoplankton or zooplankton organisms, recovered from sea floor sediments. Potential seasonal biases of paleo proxies were intensely studied in the past, however, even for the two most commonly used paleo proxies for SST, UK0 37 and Mg/Ca ratios, a clear global picture does not yet exist. In the present study we combine Holocene SST trends derived from UK0 37 and Mg/Ca ratios with results from idealized climate model simulations forced by changes in the orbital conguration, which represents the major climate driver over the last 10 kyrs. Such changes cause a spatio-temporal redistribution of incoming solar radiation resulting in a modulation of amplitude and phasing of the seasonal cycle. Considering that the climate signal recorded by a plankton-based paleo proxy may be aected by the seasonal productivity cycle of the respective organism, we use the modern relationship between SST and marine net primary production (NPP), both obtained from satellite observations, to calculate a seasonality index (SI) as an independent constraint to link modeled SST trends with proxy data. Although the climate model systematically underestimates Holocene SST trends, we find that seasonal productivity peaks of the phytoplankton-based UK0 37 result in a preferential registering of the warm (cold) season in high (low) latitudes, as it was expected from the SI distribution. The overall smoother trends from the zooplankton-derived Mg/Ca-SSTs suggest a more integrated signal over longer time averages, which may also carry a seasonal bias, but the spatial pattern is less clear. Based on our ndings, careful multi-proxy approaches can actually go beyond the reconstruction of average climate trends, specifically allowing to resolve the evolution of seasonality.

Description: A global synthesis of Miocene benthic foraminiferal carbon and oxygen isotopic and faunal abundance data indicates that Miocene thermohaline circulation evolved through three regimes corresponding approximately to early, middle, and late Miocene times. There is evidence for major qualitative differences between the circulation of the modern ocean and the Miocene ocean prior to 11 Ma. The 13C/12C ratios of the benthic foraminifera Cibicidoides are interpreted in terms of water mass aging, i.e., the progressive depletion of dissolved O2 and lowering of δ13C values as the result of oxidation of organic matter as water flows further from its sources at the surface of the oceans. Both isotopic and faunal data indicate that the early Miocene regime, from 22 to 15 Ma, was the most different from today's. During that interval intermediate and deep waters of both the Atlantic and the Pacific oceans aged in a northward direction, and the intermediate waters of the Indian, the South Atlantic and the South Pacific oceans were consistently the youngest in the global ocean. We speculate that early Miocene global thermohaline circulation may have been strongly influenced by the influx of warm saline water, Tethyan Indian Saline Water, from the Tethys into the northern Indian Ocean. The isotopic and faunal data suggest that flow from the Tethyan region into the Indian Ocean diminished or terminated at about 14 Ma. Isotopic and faunal data give no evidence for North Atlantic Deep Water (NADW) formation prior to about 14.5 Ma (with the exception of a brief episode in the early Miocene). From 14.5 to 11 Ma NADW formation was weak, and circumpolar and Antarctic water flooded the deep South Atlantic and South Pacific as the Antarctic ice cap grew. From about 10 Ma to the end of the Miocene, thermohaline circulation resembled the modern circulation in many ways. In latest Miocene time (6 to 5 Ma) circulation patterns were very similar to today's except that NADW formation was greatly diminished. The distribution pattern of siliceous oozes in Miocene sediments is consistent with our proposed reconstruction of thermohaline circulation. Major changes which occurred in circulation during the middle Miocene were probably related to the closing of the Tethys and may have contributed to rapid middle Miocene growth of the Antarctic ice cap.

Description: Variations in carbonate flux and dissolution, which occurred in the equatorial Atlantic during the last 24,000 years, have been estimated by a new approach that allows the point-by-point determination of paleofluxes to the seafloor. An unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation. The method is based on observations that the flux of unsupported 230Th into deep-sea sediments is nearly independent of the total mass flux and is close to the production rate. Thus excess 230Th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated. The study was conducted at two sites (Ceará Rise; western equatorial Atlantic, and Sierra Leone Rise; eastern equatorial Atlantic) in cores raised from three different depths at each site. From measurements of 230Th and CaCO3, changes in carbonate flux with time and depth were obtained. A rapid increase in carbonate production, starting at the onset of deglaciation, was found in both areas. This event may have important implications for the postglacial increase in atmospheric CO2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters (and possibly the North Atlantic Deep Water). Increased carbonate dissolution occurred in the two regions during deglaciation, followed by a minimum during mid-Holocene and renewed intensification of dissolution in late Holocene. During the last 16,000 years, carbonate dissolution was consistently more pronounced in the western than in the eastern basin, reflecting the influence of Antarctic Bottom Water in the west. This trend was reversed during stage 2, possibly due to the accumulation of metabolic CO2 below the level of the Romanche Fracture Zone in the eastern basin.

Description: Benthic δ18O data from 95 core sites are used to infer possible temperature-salinity (T-S) fields of the Atlantic and Pacific oceans at the Last Glacial Maximum (LGM). A constraint of stable density stratification yields logically consistent scenarios for both T and S. The solutions are not unique but are useful as a thinking tool. To better constrain the inferences drawn from the spatial distribution of benthic δ18O, we must reduce scatter in the δ18O data with more high-quality measurements in high sedimentation rate cores. Also, we must intercalibrate mass spectrometers at different isotope laboratories more accurately, to insure our isotope data are compatible.