ALBERT

Description: High resolution satellite turbidity and sea surface temperature observations of river plume interactions during a significant flood event Ocean Science Discussions, 12, 1669-1692, 2015 Author(s): V. E. Brando, F. Braga, L. Zaggia, C. Giardino, M. Bresciani, D. Bellafiore, C. Ferrarin, F. Maicu, A. Benetazzo, D. Bonaldo, F. M. Falcieri, A. Coluccelli, A. Russo, and S. Carniel Sea surface temperature (SST) and turbidity ( T ) derived from Landsat-8 (L8) imagery were used to characterize river plumes in the Northern Adriatic Sea (NAS) during a significant flood event in November 2014. Sea surface salinity (SSS) from an operational coupled ocean-wave model supported the interpretation of the plumes interaction with the receiving waters and among them. There was a good agreement of the SSS, T , and SST fields at the sub-mesoscale and mesoscale delineation of the major river plumes. L8 30 m resolution enabled also the description of smaller plume structures. Sharp fronts in T and SST delimited each single river plume. The isotherms and turbidity isolines coupling varied among the plumes due to differences in particle loads and surface temperatures in the discharged waters. The different plumes reflectance spectra were related to the lithological fingerprint of the sediments in the river catchments.

Description: Spatial scales of temperature and salinity variability estimated from Argo observations Ocean Science Discussions, 12, 1793-1814, 2015 Author(s): F. Ninove, P. Y. Le Traon, E. Remy, and S. Guinehut Argo observations from 2005 to 2013 are used to characterize spatial scales temperature and salinity variations from the surface down to 1500 m. Simulations are first performed to analyze the sensitivity of results to Argo sampling; they show that several years of Argo observations are required to estimate the spatial scales of ocean variability over 20° × 20° boxes. Spatial scales are then computed over several large scale areas. Zonal and meridional spatial scales ( Lx and Ly which are also zero crossing of covariance functions) vary as expected with latitudes. Scales are of about 100 km at high latitudes and more of 700 km in the Indian and Pacific equatorial/tropical regions. Zonal and meridional scales are similar: except in these tropical/equatorial regions where zonal scales are much larger (by a factor of 2 to 3) than meridional scales. Spatial scales are the largest close to the surface and have a general tendency for temperature to increase in deeper layers. There are significant differences between temperature and salinity scales, in particular, in the deep ocean. Results are consistent with previous studies based on sparse in-situ observations or satellite altimetry. They provide, however, for the first time a global description of temperature and salinity scales of variability and a characterization of their variations according to depths.

Description: A semi-analytical model for diffuse reflectance in marine and inland waters Ocean Science Discussions, 12, 1893-1912, 2015 Author(s): J. D. Pravin, P. Shanmugam, and Y.-H. Ahn A semi-analytical model for predicting diffuse reflectance of coastal and oceanic waters is developed based on the water-column optical properties and illumination conditions. Diffuse reflectance ( R ) is an apparent optical property that is related to the Gordon's parameter ( b b /(a+b b ) ) through a proportionality factor " f ". The conventional assumption of " f " as a constant (0.33) yields large errors in case of turbid and productive coastal waters and a predictive model based on this assumption is generally restricted to open-ocean waters (low chlorophyll case). In this paper, we have sorted the dependent factors that influence " f " values in the water column. Here, the parameter " f " is modeled as a function of wavelength, depth, inherent optical properties (IOPs) and illumination conditions. This work eliminates the spectral constants ( K Chl and K SS ) associated with our previous model and constrains the present model to be solely dependent on the IOPs and illumination conditions. Data used for parameterization and validation are obtained from in situ measurements in different waters within coastal environments. Validation shows good agreement between the model R and in situ R values with the overall mean relative error of less than a few percent. The model is valid for a wide range waters within coastal and open-ocean environments.

Description: Impact of variable sea-water conductivity on motional induction simulated with an OGCM Ocean Science Discussions, 12, 1869-1891, 2015 Author(s): C. Irrgang, J. Saynisch, and M. Thomas Carrying high concentrations of dissolved salt, ocean water is a good electrical conductor. As sea-water flows through the Earth's ambient geomagnetic field, electric fields are generated, which in turn induce secondary magnetic fields. In current models for oceanic induced magnetic fields, a realistic consideration of sea-water conductivity is often neglected and the effect on the variability of the oceanic induced magnetic field unknown. To model magnetic fields that are induced by non-tidal global ocean currents, an electromagnetic induction model is implemented into the Ocean Model for Circulation and Tides (OMCT). This provides the opportunity to not only model oceanic induced magnetic signals, but to assess the impact of oceanographic phenomena on the induction process. In this paper, the sensitivity of the induction process due to spatial and temporal variations in sea-water conductivity is investigated. It is shown that assuming an ocean-wide uniform conductivity is insufficient to accurately capture the temporal variability of the magnetic signal. Using instead a realistic global sea-water conductivity distribution increases the temporal variability of the magnetic field up to 45 %. Especially vertical gradients in sea-water conductivity prove to be a key factor for the variability of the oceanic induced magnetic field. However, temporal variations of sea-water conductivity only marginally affect the magnetic signal.

Description: Design and validation of MEDRYS, a Mediterranean Sea reanalysis over 1992–2013 Ocean Science Discussions, 12, 1815-1867, 2015 Author(s): M. Hamon, J. Beuvier, S. Somot, J. M. Lellouche, E. Greiner, G. Jordà, M. N. Bouin, T. Arsouze, K. Béranger, F. Sevault, C. Dubois, M. Drevillon, and Y. Drillet The French research community on the Mediterranean Sea modelling and the French operational ocean forecasting center Mercator Océan have gathered their skill and expertise in physical oceanography, ocean modelling, atmospheric forcings and data assimilation, to carry out a MEDiterranean sea ReanalYsiS (MEDRYS) at high resolution for the period 1992–2013. The ocean model used is NEMOMED12, a Mediterranean configuration of NEMO with a 1/12° (∼ 7 km) horizontal resolution and 75 vertical z levels with partial steps. At the surface, it is forced by a new atmospheric forcing dataset (ALDERA), coming from a dynamical downscaling of the ERA-Interim atmospheric reanalysis by the regional climate model ALADIN-Climate with a 12 km horizontal and 3 h temporal resolutions. This configuration is used to carry a 34 year free simulation over the period 1979–2013 (NM12-FREE) which is the initial state of the reanalysis in October 1992. The first version of MEDRYS uses the existing Mercator Océan data assimilation system SAM that is based on a reduced-order Kalman filter with a 3-D multivariate modal decomposition of the forecast error. Altimeter data, satellite SST and temperature and salinity vertical profiles are jointly assimilated. This paper describes the configuration we used to perform the MEDRYS simulation. We then first validate the skills of the data assimilation system. It is shown that the data assimilation restores a good averaged temperature and salinity in intermediate layers compared to the free simulation. No particular biases are identified in the bottom layers. However, the reanalysis show slight positive biases of 0.02 psu and 0.15 °C above 150 m depth. In the validation stage, it is also shown that the assimilation allows to better reproduce water, heat and salt transports through the Strait of Gibraltar. Finally, the ability of the reanalysis to represent the sea surface high frequency variability is pointed out.

Description: Technical Note: Could benzalkonium chloride be a suitable alternative to mercuric chloride for preservation of seawater samples? Ocean Science Discussions, 12, 1953-1969, 2015 Author(s): J. Gloël, C. Robinson, G. H. Tilstone, G. Tarran, and J. Kaiser Instrumental equipment unsuitable or unavailable for fieldwork as well as lack of ship space can necessitate the preservation of seawater samples prior to analysis in a shore-based laboratory. Mercuric chloride (HgCl 2 ) is routinely used for such preservation, but its handling and subsequent disposal incur significant risks and expense. Benzalkonium chloride (BAC) has been used previously for freshwater samples. Here, we assess BAC as a less hazardous alternative microbial inhibitor for marine samples prior to the measurement of oxygen-to-argon (O 2 /Ar) ratios, as used for the determination of plankton net community production. BAC at a concentration of 50 mg dm −3 inhibited microbial activity for at least three days in seawater with chlorophyll a (Chl a ) concentrations up to 1 mg m −3 , possibly longer when Chl a concentrations were lower. BAC concentrations of 100 and 200 mg dm −3 were no more effective than 50 mg dm −3 . With fewer risks to human health and the environment, and no requirement for expensive waste disposal, BAC could be a viable alternative to HgCl 2 for short-term preservation of seawater samples, but is not a replacement for HgCl 2 in the case of oxygen triple isotope analysis, which requires storage over weeks to months. In any event, further tests on a case-by-case basis should be undertaken if use of BAC was considered, since its inhibitory activity may depend on concentration and composition of the microbial community.

Description: Turbulence observations in the Gulf of Trieste under moderate wind forcing and different water column stratification Ocean Science Discussions, 12, 1729-1764, 2015 Author(s): F. M. Falcieri, L. Kantha, A. Benetazzo, A. Bergamasco, D. Bonaldo, F. Barbariol, V. Malačič, M. S. Sclavo, and S. Carniel During the oceanographic campaign CARPET2014, between 30 January and 4 February 2014, a total of 478 microstructure profiles (grouped into 145 ensembles) and 38 CTD casts were made in the Gulf of Trieste (Northern Adriatic Sea) under moderate wind forcing (average wind speed 10 m s -1 ) and heat fluxes (net negative heat flux in the range of 150 to 400 W m -2 ). Among the collected profiles, there were three sets of yoyo casts, each lasting for about 12 h for a total of 50 casts. Overall, these represent the first turbulence observations collected in the Gulf of Trieste. Microstructure profiles collected with a free-falling profiler must be taken in enables of repeated casts, with the objective of obtaining more statistically significant values for turbulence parameters. This approach is certainly feasible in shallow waters, but has a down side when the vertical density structure includes strong interfaces that can move up or down between subsequent casts, under the influence of tides and internal waves. In order to minimize the smearing effect of such interfacial displacements on mean quantities, we developed an algorithm to realign, according to the temperature profile, successive microstructure profiles to produce sharper and more meaningful mean profiles of measured turbulence parameters. During CARPET2014, the water column in the Gulf evolved from a well-mixed condition to a stratified one, due to Adriatic waters intruding at the bottom along the Gulf's south-eastern coast. These waters stratified the water column and changed its stability characteristics, which in turn prevented wind driven turbulence from penetrating to the bottom of the water column. In this study, we show that during a warm and relatively dry winter, such as in 2014, the Gulf of Trieste was not completely mixed because of the influence of bottom waters intruding from the open sea, even under moderate wind forcing. Inside the Gulf, two types of water intrusions from the Adriatic Sea were observed during the yoyo casts: one coming from its northern coast (i.e. warmer, saltier and more turbid) and one coming from the open sea in front of the Po Delta (i.e. cooler, fresher and less turbid). Those two intrusions behaved similarly but had a different impact on turbulence kinetic energy dissipation rate profiles. The former, with high turbidity, acted as a barrier to wind-driven turbulence, while the latter, with low sediment concentrations and a smaller density gradient when compared to the rest of the water column, was not able to suppress downward penetration of turbulence from the surface to the same degree.

Description: Monitoring Atlantic overturning circulation variability with GRACE-type ocean bottom pressure observations – a sensitivity study Ocean Science Discussions, 12, 1765-1791, 2015 Author(s): K. Bentel, F. W. Landerer, and C. Boening The Atlantic Meridional Overturning Circulation (AMOC) is a key mechanism for large-scale northward heat transport and thus plays an important role for global climate. Relatively warm water is transported northward in the upper layers of the North Atlantic Ocean, and after cooling at subpolar latitudes, sinks down and is transported back south in the deeper limb of the AMOC. The utility of in-situ ocean bottom pressure (OBP) observations to infer AMOC changes at single latitudes has been characterized in recent literature using output from ocean models. We extend the analysis and examine the utility of space-based observations of time-variable gravity and the inversion for ocean bottom pressure to monitor AMOC changes and variability between 20 and 60° N. Consistent with previous results, we find a strong correlation between the AMOC signal and OBP variations, mainly along the western slope of the Atlantic basin. We then use synthetic OBP data – smoothed and filtered to resemble the resolution of the GRACE gravity mission – and reconstruct geostrophic AMOC transport. Due to the coarse resolution of GRACE-like OBP fields, we find that leakage of signal across the step slopes of the ocean basin is a significant challenge at certain latitudes. However, overall, the inter-annual AMOC anomaly time series can be recovered from 20 years of monthly GRACE-like OBP fields with errors less than 1 Sverdrup.

Description: A collection of sub-daily pressure and temperature observations for the early instrumental period with a focus on the "year without a summer" 1816 Climate of the Past, 11, 1027-1047, 2015 Author(s): Y. Brugnara, R. Auchmann, S. Brönnimann, R. J. Allan, I. Auer, M. Barriendos, H. Bergström, J. Bhend, R. Brázdil, G. P. Compo, R. C. Cornes, F. Dominguez-Castro, A. F. V. van Engelen, J. Filipiak, J. Holopainen, S. Jourdain, M. Kunz, J. Luterbacher, M. Maugeri, L. Mercalli, A. Moberg, C. J. Mock, G. Pichard, L. Řezníčková, G. van der Schrier, V. Slonosky, Z. Ustrnul, M. A. Valente, A. Wypych, and X. Yin The eruption of Mount Tambora (Indonesia) in April 1815 is the largest documented volcanic eruption in history. It is associated with a large global cooling during the following year, felt particularly in parts of Europe and North America, where the year 1816 became known as the "year without a summer". This paper describes an effort made to collect surface meteorological observations from the early instrumental period, with a focus on the years of and immediately following the eruption (1815–1817). Although the collection aimed in particular at pressure observations, correspondent temperature observations were also recovered. Some of the series had already been described in the literature, but a large part of the data, recently digitised from original weather diaries and contemporary magazines and newspapers, is presented here for the first time. The collection puts together more than 50 sub-daily series from land observatories in Europe and North America and from ships in the tropics. The pressure observations have been corrected for temperature and gravity and reduced to mean sea level. Moreover, an additional statistical correction was applied to take into account common error sources in mercury barometers. To assess the reliability of the corrected data set, the variance in the pressure observations is compared with modern climatologies, and single observations are used for synoptic analyses of three case studies in Europe. All raw observations will be made available to the scientific community in the International Surface Pressure Databank.

Description: Bottom water variability in the subtropical northwestern Pacific from 26 kyr BP to present based on Mg / Ca and stable carbon and oxygen isotopes of benthic foraminifera Climate of the Past, 11, 803-824, 2015 Author(s): Y. Kubota, K. Kimoto, T. Itaki, Y. Yokoyama, Y. Miyairi, and H. Matsuzaki To understand bottom water variability in the subtropical northwestern Pacific, bottom water temperatures (BWTs), carbon isotopes (δ 13 C), and oxygen isotopes of seawater (δ 18 O w ) at a water depth of 1166 m were reconstructed from 26 kyr BP to present. A new regional Mg / Ca calibration for the benthic foraminifera Cibicidoides wuellerstorfi (type B) was established to convert the benthic Mg / Ca value to BWT, based on 26 surface sediment samples and two core-top samples retrieved around Okinawa Island. During the Last Glacial Maximum (LGM), the δ 18 O w in the intermediate water in the northwestern South Pacific was ~0.4‰ lower than in the deep South Pacific, indicating a greater vertical salinity gradient than at present. This salinity (and probably density) structure would have led to stratification in the intermediate and deep Pacific, which would, in turn, have greatly influenced carbon storage during the glacial time. The benthic Mg / Ca and δ 18 O w records suggest changes that seem to follow Heinrich event 1 (H1) and the Bølling–Alleød (B/A) and Younger Dryas (YD) intervals, with BWT higher during H1 (~17 kyr BP) and YD (~12 kyr BP) and lower during B/A (~14 kyr BP). The warming in the bottom water during H1 suggests increased contribution of North Pacific Intermediate Water (NPIW) to the subtropical northwestern Pacific and decreased upwelling of cooler waters from the abyssal North Pacific. During the interval from 17 to 14.5 kyr BP, the BWT tended to decrease successively in association with a decrease in δ 13 C values, presumably as a result of increased upwelling of the abyssal waters to the intermediate depths of the North Pacific caused by shoaling and enhancement of the southward return flow of Pacific Deep Water (PDW). During the Holocene, the millennial- to sub-millennial-scale variations in the BWT generally correlate with the sea surface temperatures in the Okhotsk Sea, the source region of the NPIW, suggesting that changes in the BWT are linked to changes in the NPIW production rate.

Description: An improved method for the determination of dissolved nitric oxide (NO) in seawater samples Ocean Science Discussions, 12, 959-981, 2015 Author(s): H. E. Lutterbeck and H. W. Bange Nitric oxide (NO) is a short-lived intermediate of the oceanic nitrogen cycle, however, due to its high reactivity, measurements of dissolved NO in seawater are rare. Here we present an improved method to determine NO concentrations in discrete seawater samples. The set-up of our system consisted of a chemiluminescence NO analyser connected to a stripping unit. The limit of detection for our method was 5 pmol NO in aqueous solution which translates into 0.25 nmol L −1 when using a 20 mL seawater sample volume. Our method was applied to measure high resolution depth profiles of dissolved NO during a cruise to the eastern tropical South Pacific Ocean. Our method is fast and comparably easy to handle thus it opens the door for deciphering the distribution of NO in the ocean and it facilitates laboratory studies on NO pathways.

Description: Regime changes in global sea surface salinity trend Ocean Science Discussions, 12, 983-1011, 2015 Author(s): A. L. Aretxabaleta, K. W. Smith, and J. Ballabrera-Poy Recent studies have shown significant sea surface salinity (SSS) changes at scales ranging from regional to global. In this study, we estimate global salinity means and trends using historical (1950–2014) SSS data from the UK Met. Office Hadley Centre objectively analyzed monthly fields and recent data from the SMOS satellite (2010–2014). We separate the different components (regimes) of the global surface salinity by fitting a Gaussian Mixture Model to the data and using Expectation–Maximization to distinguish the means and trends of the data. The procedure uses a non-subjective method (Bayesian Information Criterion) to extract the optimal number of means and trends. The results show the presence of three separate regimes: Regime A (1950–1990) is characterized by small trend magnitudes; Regime B (1990–2009) exhibited enhanced trends; and Regime C (2009–2014) with significantly larger trend magnitudes. The salinity differences between regime means were around 0.01. The trend acceleration could be related to an enhanced global hydrological cycle or to a change in the sampling methodology.

Description: Investigation of model capability in capturing vertical hydrodynamic coastal processes: a case study in the North Adriatic Sea Ocean Science Discussions, 12, 1625-1668, 2015 Author(s): W. J. McKiver, G. Sannino, F. Braga, and D. Bellafiore In this work we consider a numerical study of hydrodynamics in the coastal zone using two different models, SHYFEM and MITgcm, to assess their capability to capture the main processes. We focus on the North Adriatic Sea during a strong dense water event that occurred at the beginning of 2012. This serves as an interesting test case to examine both the models strengths and weaknesses, while giving an opportunity to understand how these events affect coastal processes, like upwelling and downwelling, and how they interact with estuarine dynamics. Using the models we examine the impact of setup, surface and lateral boundary treatment, resolution and mixing schemes, as well as assessing the importance of nonhydrostatic dynamics in coastal processes. Both models are able to capture the dense water event, though each displays biases in different regions. The models show large differences in the reproduction of surface patterns, identifying the choice of suitable bulk formulas as a central point for the correct simulation of the thermohaline structure of the coastal zone. Moreover, the different approaches in treating lateral freshwater sources affect the vertical coastal stratification. The results indicate the importance of having high horizontal resolution in the coastal zone, specifically in close proximity to river inputs, in order to reproduce the effect of the complex coastal morphology on the hydrodynamics. A lower resolution offshore is acceptable for the reproduction of the dense water event, even if specific vortical structures are missed. Finally, it is found that nonhydrostatic processes are of little importance for the reproduction of dense water formation in the shelf of the North Adriatic Sea.

Description: Responses of atmospheric circulation to sea surface temperature anomalies in the South China Sea Ocean Science Discussions, 12, 1693-1710, 2015 Author(s): M. Zhou and G. Wang The sea surface temperature (SST) anomalies in the South China Sea (SCS) and their influences on global atmospheric circulation were studied. The results of the simple atmospheric model suggested that the SCS SST anomalies can induce several barotropic wave trains from the SCS to other regions such as North America, high latitudes of the Southern Hemisphere and the Mediterranean. The baroclinic stream function anomalies from the simple model showed an anticyclonic vortex pair in East Asia and southern tropical Indian Ocean and a cyclonic vortex pair in the North Pacific and the Southwest Pacific. It is suggested that the spatial pattern of SST anomalies in the SCS can affect the magnitude of stream function anomalies, although it cannot affect the spatial pattern of atmospheric circulation.

Description: Technical Note: Medium-term morphodynamics in an unprotected sandy beach of the Adriatic Sea Ocean Science Discussions, 12, 1711-1728, 2015 Author(s): M. Postacchini, L. Soldini, C. Lorenzoni, and A. Mancinelli In the recent years attention has been paid to the beach protection by means of soft and hard defenses. Along the Italian coasts of the Adriatic Sea, sandy beaches are the most common landscapes and around 70 % of the Marche-Region coasts (central Adriatic), is protected by defense structures. The longest free-from-obstacle nearshore area in the Region includes the beach of Senigallia, characterized by a multiple barred beach, frequently monitored during the last decades. The bathymetries surveyed in 2006, 2010, 2011, 2012 and 2013 show a good adaptation of the beach to the Dean-type equilibrium profile, though a strong short-/medium-term variability of the wave climate has been observed during the monitored periods. This suggests a slight influence of wave forcing on the long-term profiles, which seems to only depend on the sediment size. Further, the medium-term dynamics of the submerged bars and their geometric features have been related to the wave climate collected by a wave buoy located 40 km off Senigallia during the analyzed temporal windows. An overall interpretation of the complete dynamics, i.e. hydrodynamics (buoy data), sediment characteristics (equilibrium-profile A parameter) and morphodynamics (bathymetric surveys), suggests that the wave climate is fundamental for the morphodynamic changes of the beach in the medium term: waves coming from NNE/ESE are characterized by a larger/smaller steepness and induce seaward/shoreward bar migration, as well as bar smoothing/steepening. Moving southward, the bar dimension increases, while the equilibrium profile suggests a decrease of the sediment size in the submerged beach, this probably due to the presence of both harbor jetty and river mouth North of the investigated area.

Description: The near-inertial variability of meridional overturning circulation in the South China Sea as shown by an eddy-resolving ocean reanalysis Ocean Science Discussions, 12, 2123-2146, 2015 Author(s): J. Xiao, D. Wang, Q. Xie, Y. Shu, C. Liu, and J. Chen The near-inertial variability of the meridional overturning circulation in the South China Sea (SCSMOC) has been analyzed based on a global 1/12° ocean reanalysis. The wavelet analysis and power spectrum of deep SCSMOC time series shows that there is a significant signal in the near-inertial band. The maximum amplitude of the near-inertial signal in the SCSMOC is nearly 4 Sv. The spatial structure of the signal features regularly alternating counterclockwise and clockwise overturning cells. It is also found that the near-inertial signal of SCSMOC mainly originates from the Luzon Strait and propagates equatorward with the speed of 1–3 m s −1 . Further analyses suggest that the near-inertial signal in the SCSMOC is triggered by high-frequency wind variability near the Luzon Strait where geostrophic shear always exists due to Kuroshio intrusion.

Description: Coupled Northern Hemisphere permafrost–ice-sheet evolution over the last glacial cycle Climate of the Past, 11, 1165-1180, 2015 Author(s): M. Willeit and A. Ganopolski Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2, and the coupled Northern Hemisphere (NH) permafrost–ice-sheet evolution over the last glacial cycle is explored. The model performs generally well at reproducing present-day permafrost extent and thickness. Modeled permafrost thickness is sensitive to the values of ground porosity, thermal conductivity and geothermal heat flux. Permafrost extent at the Last Glacial Maximum (LGM) agrees well with reconstructions and previous modeling estimates. Present-day permafrost thickness is far from equilibrium over deep permafrost regions. Over central Siberia and the Arctic Archipelago permafrost is presently up to 200–500 m thicker than it would be at equilibrium. In these areas, present-day permafrost depth strongly depends on the past climate history and simulations indicate that deep permafrost has a memory of surface temperature variations going back to at least 800 ka. Over the last glacial cycle permafrost has a relatively modest impact on simulated NH ice sheet volume except at LGM, when including permafrost increases ice volume by about 15 m sea level equivalent in our model. This is explained by a delayed melting of the ice base from below by the geothermal heat flux when the ice sheet sits on a porous sediment layer and permafrost has to be melted first. Permafrost affects ice sheet dynamics only when ice extends over areas covered by thick sediments, which is the case at LGM.

Description: Recent transient tracer distributions in the Fram Strait: estimation of anthropogenic carbon content and transport Ocean Science Discussions, 12, 2189-2229, 2015 Author(s): T. Stöven, T. Tanhua, M. Hoppema, and W.-J. von Appen The storage of anthropogenic carbon in the ocean's interior is an important process which modulates the increasing carbon dioxide concentrations in the atmosphere. The polar regions are expected to be net sinks for anthropogenic carbon. Transport estimates of dissolved inorganic carbon and the anthropogenic offset can thus provide information about the magnitude of the corresponding storage processes. Here we present a transient tracer, dissolved inorganic carbon (DIC) and total alkalinity (TA) data set along 78°50′ N sampled in the Fram Strait in 2012. A theory on tracer relationships is introduced which allows for an application of the Inverse Gaussian – Transit Time Distribution (IG-TTD) at high latitudes and the estimation of anthropogenic carbon concentrations. Current velocity measurements along the same section were used to estimate the net flux of DIC and anthropogenic carbon through the Fram Strait. The new theory explains the differences between the theoretical (IG-TTD based) tracer age relationship and the specific tracer age relationship of the field data by saturation effects during water mass formation and/or the deliberate release experiment of SF 6 in the Greenland Sea in 1996 rather than by different mixing or ventilation processes. Based on this assumption, a maximum SF 6 excess of 0.5–0.8 fmol kg −1 was determined in the Fram Strait at intermediate depths (500–1600 m). The anthropogenic carbon concentrations are 50–55 μmol kg −1 in the Atlantic Water/Recirculating Atlantic Water, 40–45 μmol kg −1 in the Polar Surface Water/warm Polar Surface Water and between 10–35 μmol kg −1 in the deeper water layers, with lowest concentrations in the bottom layer. The net DIC and anthropogenic carbon fluxes through the Fram Strait indicate a balanced exchange between the Arctic Ocean and the North Atlantic, although with high uncertainties.

Description: Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes Climate of the Past, 11, 1197-1222, 2015 Author(s): P. J. Bartlein, M. E. Edwards, S. W. Hostetler, S. L. Shafer, P. M. Anderson, L. B. Brubaker, and A. V. Lozhkin Arctic land-cover changes induced by recent global climate change (e.g., expansion of woody vegetation into tundra and effects of permafrost degradation) are expected to generate further feedbacks to the climate system. Past changes can be used to assess our understanding of feedback mechanisms through a combination of process modeling and paleo-observations. The subcontinental region of Beringia (northeastern Siberia, Alaska, and northwestern Canada) was largely ice-free at the peak of deglacial warming and experienced both major vegetation change and loss of permafrost when many arctic regions were still ice covered. The evolution of Beringian climate at this time was largely driven by global features, such as the amplified seasonal cycle of Northern Hemisphere insolation and changes in global ice volume and atmospheric composition, but changes in regional land-surface controls, such as the widespread development of thaw lakes, the replacement of tundra by deciduous forest or woodland, and the flooding of the Bering–Chukchi land bridge, were probably also important. We examined the sensitivity of Beringia's early Holocene climate to these regional-scale controls using a regional climate model (RegCM). Lateral and oceanic boundary conditions were provided by global climate simulations conducted using the GENESIS V2.01 atmospheric general circulation model (AGCM) with a mixed-layer ocean. We carried out two present-day simulations of regional climate – one with modern and one with 11 ka geography – plus another simulation for 6 ka. In addition, we performed five ~ 11 ka climate simulations, each driven by the same global AGCM boundary conditions: (i) 11 ka Control , which represents conditions just prior to the major transitions (exposed land bridge, no thaw lakes or wetlands, widespread tundra vegetation), (ii) sea-level rise, which employed present-day continental outlines, (iii) vegetation change, with deciduous needleleaf and deciduous broadleaf boreal vegetation types distributed as suggested by the paleoecological record, (iv) thaw lakes, which used the present-day distribution of lakes and wetlands, and (v) post-11 ka All , incorporating all boundary conditions changed in experiments (ii)–(iv). We find that regional-scale controls strongly mediate the climate responses to changes in the large-scale controls, amplifying them in some cases, damping them in others, and, overall, generating considerable spatial heterogeneity in the simulated climate changes. The change from tundra to deciduous woodland produces additional widespread warming in spring and early summer over that induced by the 11 ka insolation regime alone, and lakes and wetlands produce modest and localized cooling in summer and warming in winter. The greatest effect is the flooding of the land bridge and shelves, which produces generally cooler conditions in summer but warmer conditions in winter and is most clearly manifest on the flooded shelves and in eastern Beringia. By 6 ka continued amplification of the seasonal cycle of insolation and loss of the Laurentide ice sheet produce temperatures similar to or higher than those at 11 ka, plus a longer growing season.

Description: The dynamic connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current Ocean Science Discussions, 12, 2231-2256, 2015 Author(s): E. Lambert, D. Le Bars, and W. P. M. de Ruijter East of Madagascar, wind and surface buoyancy fluxes reinforce each other, leading to frontogenesis, outcrop and an eastward along-front flow: the South Indian Ocean Countercurrent (SICC). In the east the Leeuwin Current (LC) is a unique eastern boundary current which flows poleward along Australia. It is often described as a regional coastal current forced by an off-shore meridional density gradient or a sea surface slope, yet little is known of the forcing and dynamics that control these open ocean meridional gadients. To complete this understanding, we make use of both an ocean general circulation model and a conceptual two-layer model. The SICC impinges on west Australia and adds to a sea level slope and a southward geostrophic coastal jet: the Leeuwin Current. The SICC and the LC are thus dynamically connected. An observed transport maximum of the LC around 22° S is directly related to this impingement of the SICC. The circulation of the Indonesian Throughflow (ITF) through the Indian Ocean appears to be partly trapped in the upper layer north of the outcrop line and is redirected along this outcrop line to join the eastward flow of the SICC. Shutdown of the ITF in both models strongly decreases the Leeuwin Current transport and breaks the connection between the LC and SICC. In this case, most of the SICC was found to reconnect to the internal gyre circulation in the Indian Ocean. The Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current are thus dynamically coupled.

Description: Impact of vertical and horizontal advection on nutrient distribution in the South East Pacific Ocean Science Discussions, 12, 2257-2281, 2015 Author(s): B. Barceló-Llull, E. Mason, and A. Pascual An innovative approach is used to analyse the impact of vertical velocities associated with quasi-geostrophic (QG) dynamics on the distribution of a passive nutrient tracer (nitrate) in the South East Pacific. Twelve years of vertical and horizontal currents are derived from an observation-based estimate of the ocean state. Horizontal velocities are obtained through application of thermal wind balance to weekly temperature and salinity fields. Vertical velocities are estimated by integration of the QG Omega equation. Seasonal variability of the synthetic vertical velocity and kinetic energy associated with the horizontal currents are coincident, with peaks in austral summer (November–December) in accord with published observations. Two ensembles of Lagrangian particle tracking experiments that differ according to vertical forcing ( w = w QG vs. w = 0) enable a quantitative analysis of the impact of the vertical velocity. From identical initial distributions of nitrate-tagged particles, the Lagrangian results show that the impact of vertical advection on nutrient distribution is 30 % of the contribution of horizontal advection. Despite being weaker by a factor of up to 10 −4 than the horizontal currents, vertical velocity is demonstrated to make an important contribution to nutrient distributions in the region of study.

Description: Imprint of external climate forcing on coastal upwelling in past and future climate Ocean Science Discussions, 12, 2899-2930, 2015 Author(s): N. Tim, E. Zorita, B. Hünicke, X. Yi, and K.-C. Emeis The Eastern Boundary Upwelling Systems are the major coastal upwelling regions. The trade winds are driving these upwelling regimes located in the subtropics at the eastern boundary of the Atlantic and Pacific Ocean. Here we analyse the impact of the external climate forcing, e.g. the greenhouse gas concentration, solar activity and volcano eruptions, on these upwelling systems in simulations of ensembles of two Earth System Models. The ensembles contain three simulations for each time period which cover the past millennium (900–1850), the 20th century (1850–2005) and the near future (2006–2100). Using a set of simulations, differing only in their initial conditions, enables us to detect whether the variability is driven internally or externally. Our analysis shows that the variability of the simulated upwelling is to the most driven internally and that there are no significant trends except for the scenario with the most dramatic increase of greenhouse gas concentrations.

Description: Transitivity of the climate–vegetation system in a warm climate Climate of the Past, 11, 1563-1574, 2015 Author(s): U. Port and M. Claussen To date, the transitivity of the global system has been analysed for late Quaternary (glacial, interglacial, and present-day) climate. Here, we extend this analysis to a warm, almost ice-free climate with a different configuration of continents. We use the Earth system model of the Max Planck Institute for Meteorology to analyse the stability of the climate system under early Eocene and pre-industrial conditions. We initialize the simulations by prescribing either dense forests or bare deserts on all continents. Starting with desert continents, an extended desert remains in central Asia in the early Eocene climate. Starting with dense forest coverage, the Asian desert is much smaller, while coastal deserts develop in the Americas which appear to be larger than in the simulations with initially bare continents. These differences can be attributed to differences in the large-scale tropical circulation. With initially forested continents, a stronger dipole in the 200 hPa velocity potential develops than in the simulation with initially bare continents. This difference prevails when vegetation is allowed to adjust to and interact with climate. Further simulations with initial surface conditions that differ in the region of the Asian desert only indicate that local feedback processes are less important in the development of multiple states. In the interglacial, pre-industrial climate, multiple states develop only in the Sahel region. There, local climate–vegetation interaction seems to dominate.

Description: Upwelling characteristics in the Gulf of Finland (Baltic Sea) as revealed by Ferrybox measurements in 2007–2013 Ocean Science Discussions, 12, 2863-2898, 2015 Author(s): V. Kikas and U. Lips Ferrybox measurements are carried out between Tallinn and Helsinki in the Gulf of Finland (Baltic Sea) in a regular basis since 1997. The system measures autonomously water temperature, salinity, chlorophyll a fluorescence and turbidity and takes water samples for further analyses at a pre-defined time interval. We aimed to show how the Ferrybox technology could be used to study the coastal upwelling events in the Gulf of Finland. Based on the introduced upwelling index and related criterion, 33 coastal upwelling events were identified in May–September 2007–2013. The number of events as well as frequency of their occurrence and intensity, expressed as a sum of daily average temperature deviations in the 20 km wide coastal area, were almost equal near the northern and southern coast. It is shown that the wind impulse needed to generate upwelling events of similar intensity differ between the two coastal areas whereas this difference is related to the average wind forcing in the area. Two types of upwelling events were identified – one characterized by a strong temperature front and the other revealing gradual decrease of temperature from the open to coastal area with maximum temperature deviation close to the shore.

Description: Tidal elevation, current and energy flux in the area between the South China Sea and Java Sea Ocean Science Discussions, 12, 2831-2861, 2015 Author(s): Z. X. Wei, G. H. Fang, R. D. Susanto, T. R. Adi, B. Fan, A. Setiawan, S. J. Li, Y. G. Wang, and X. M. Gao The South China Sea (SCS) and the Java Sea (JS) are connected through the Karimata Strait, Gaspar Strait, and the southern Natuna Sea, where the tides are often used as open boundary condition for tidal simulation in the SCS or Indonesian seas. Tides, tidal currents and tidal energy fluxes of the principle constituents K 1 , O 1 , Q 1 , M 2 , S 2 and N 2 at five stations in this area have been analyzed using in-situ observational data. The results show that the diurnal tides are the dominant constituents in the entire study area. The constituent K 1 has the largest amplitude, exceeding 50 cm, whereas the amplitudes of M 2 are smaller than 5 cm at all stations. The amplitudes of S 2 may exceed M 2 in Karimata and Gaspar Straits. Tidal currents are mostly of rectilinear type in this area. The major semi axis lengths of the diurnal tidal current ellipses are about 10 cm s −1 , and those of the semi-diurnal tidal currents are smaller than 5 cm s −1 . The diurnal tidal energy flows from the SCS to the JS. The semi-diurnal tidal energy flows from the SCS to the JS through the Karimata Strait and the eastern part of the southern Natuna Sea but flows in the opposite direction in the Gaspar Strait and the western part of the southern Natuna Sea. Harmonic analysis of sea level and current observation also suggest that the study area is located in the loop band of the diurnal tidal waves, and in the nodal band of the semi-diurnal tidal waves. Comparisons show that the existing models are basically consistent with the observational results, but further improvements are necessary.

Description: How might the North American ice sheet influence the northwestern Eurasian climate? Climate of the Past, 11, 1467-1490, 2015 Author(s): P. Beghin, S. Charbit, C. Dumas, M. Kageyama, and C. Ritz It is now widely acknowledged that past Northern Hemisphere ice sheets covering Canada and northern Europe at the Last Glacial Maximum (LGM) exerted a strong influence on climate by causing changes in atmospheric and oceanic circulations. In turn, these changes may have impacted the development of the ice sheets themselves through a combination of different feedback mechanisms. The present study is designed to investigate the potential impact of the North American ice sheet on the surface mass balance (SMB) of the Eurasian ice sheet driven by simulated changes in the past glacial atmospheric circulation. Using the LMDZ5 atmospheric circulation model, we carried out 12 experiments under constant LGM conditions for insolation, greenhouse gases and ocean. In these experiments, the Eurasian ice sheet is removed. The 12 experiments differ in the North American ice-sheet topography, ranging from a white and flat (present-day topography) ice sheet to a full-size LGM ice sheet. This experimental design allows the albedo and the topographic impacts of the North American ice sheet onto the climate to be disentangled. The results are compared to our baseline experiment where both the North American and the Eurasian ice sheets have been removed. In summer, the sole albedo effect of the American ice sheet modifies the pattern of planetary waves with respect to the no-ice-sheet case, resulting in a cooling of the northwestern Eurasian region. By contrast, the atmospheric circulation changes induced by the topography of the North American ice sheet lead to a strong decrease of this cooling. In winter, the Scandinavian and the Barents–Kara regions respond differently to the American ice-sheet albedo effect: in response to atmospheric circulation changes, Scandinavia becomes warmer and total precipitation is more abundant, whereas the Barents–Kara area becomes cooler with a decrease of convective processes, causing a decrease of total precipitation. The gradual increase of the altitude of the American ice sheet leads to less total precipitation and snowfall and to colder temperatures over both the Scandinavian and the Barents and Kara sea sectors. We then compute the resulting annual surface mass balance over the Fennoscandian region from the simulated temperature and precipitation fields used to force an ice-sheet model. It clearly appears that the SMB is dominated by the ablation signal. In response to the summer cooling induced by the American ice-sheet albedo, high positive SMB values are obtained over the Eurasian region, leading thus to the growth of an ice sheet. On the contrary, the gradual increase of the American ice-sheet altitude induces more ablation over the Eurasian sector, hence limiting the growth of Fennoscandia. To test the robustness of our results with respect to the Eurasian ice sheet state, we carried out two additional LMDZ experiments with new boundary conditions involving both the American (flat or full LGM) and high Eurasian ice sheets. The most striking result is that the Eurasian ice sheet is maintained under full-LGM North American ice-sheet conditions, but loses ~ 10 % of its mass compared to the case in which the North American ice sheet is flat. These new findings qualitatively confirm the conclusions from our first series of experiments and suggest that the development of the Eurasian ice sheet may have been slowed down by the growth of the American ice sheet, offering thereby a new understanding of the evolution of Northern Hemisphere ice sheets throughout glacial–interglacial cycles.

Description: A 500-year seasonally resolved δ 18 O and δ 13 C, layer thickness and calcite aspect record from a speleothem deposited in the Han-sur-Lesse cave, Belgium Climate of the Past, 11, 789-802, 2015 Author(s): M. Van Rampelbergh, S. Verheyden, M. Allan, Y. Quinif, H. Cheng, L. R. Edwards, E. Keppens, and P. Claeys Speleothem δ 18 O and δ 13 C signals enable climate reconstructions at high resolution. However, scarce decadal and seasonally resolved speleothem records are often difficult to interpret in terms of climate due to the multitude of factors that affect the proxy signals. In this paper, a fast-growing (up to 2 mm yr −1 ) seasonally laminated speleothem from the Han-sur-Lesse cave (Belgium) is analyzed for its δ 18 O and δ 13 C values, layer thickness and changes in calcite aspect. The studied record covers the period between AD 2001 and 1479 as indicated by layer counting and confirmed by 20 U / Th ages. The Proserpine proxies are seasonally biased and document drier (and colder) winters on multidecadal scales. Higher δ 13 C signals reflect increased prior calcite precipitation (PCP) and lower soil activity during drier (and colder) winters. Thinner layers and darker calcite relate to slower growth and exist during drier (and colder) winter periods. Exceptionally dry (and cold) winter periods occur from 1565 to 1610, at 1730, from 1770 to 1800, from 1810 to 1860, and from 1880 to 1895 and correspond to exceptionally cold periods in historical and instrumental records as well as European winter temperature reconstructions. More relative climate variations, during which the four measured proxies vary independently and display lower amplitude variations, occur between 1479 and 1565, between 1610 and 1730, and between 1730 and 1770. The winters during the first and last periods are interpreted as relatively wetter (and warmer) and correspond to warmer periods in historical data and in winter temperature reconstructions in Europe. The winters in the period between 1610 and 1730 are interpreted as relatively drier (and cooler) and correspond to generally colder conditions in Europe. Interpretation of the seasonal variations in δ 18 O and δ 13 C signals differs from that on a decadal and multidecadal scale. Seasonal δ 18 O variations reflect cave air temperature variations and suggest a 2.5 °C seasonality in cave air temperature during the two relatively wetter (and warmer) winter periods (1479–1565 and 1730–1770), which corresponds to the cave air temperature seasonality observed today. Between 1610 and 1730, the δ 18 O values suggest a 1.5 °C seasonality in cave air temperature, indicating colder summer temperatures during this drier (and cooler) interval. The δ 13 C seasonality is driven by PCP and suggests generally lower PCP seasonal effects between 1479 and 1810 compared to today. A short interval of increased PCP seasonality occurs between 1600 and 1660, and reflects increased PCP in summer due to decreased winter recharge.

Description: The open boundary equation Ocean Science Discussions, 12, 925-958, 2015 Author(s): D. Diederen, H. H. G. Savenije, and M. Toffolon We present a new equation describing the hydrodynamics in infinitely long tidal channels (i.e., no reflection) under the influence of oceanic forcing. The proposed equation is a simple relationship between partial derivatives of water level and velocity. It is formally derived for a progressive wave in a frictionless, prismatic, tidal channel with a horizontal bed. Assessment of a large number of numerical simulations, where an open boundary condition is posed at a certain distance landward, suggests that it can also be considered accurate in the more natural case of converging estuaries with nonlinear friction and a bed slope. The equation follows from the open boundary condition and is therefore a part of the problem formulation for an infinite tidal channel. This finding provides a practical tool for evaluating tidal wave dynamics, by reconstructing the temporal variation of the velocity based on local observations of the water level, providing a fully local open boundary condition and allowing for local friction calibration.

Description: Controls on fire activity over the Holocene Climate of the Past, 11, 781-788, 2015 Author(s): S. Kloster, T. Brücher, V. Brovkin, and S. Wilkenskjeld Changes in fire activity over the last 8000 years are simulated with a global fire model driven by changes in climate and vegetation cover. The changes were separated into those caused through variations in fuel availability, fuel moisture or wind speed, which react differently to changes in climate. Disentangling these controlling factors helps in understanding the overall climate control on fire activity over the Holocene. Globally the burned area is simulated to increase by 2.5% between 8000 and 200 cal yr BP, with larger regional changes compensating nearly evening out on a global scale. Despite the absence of anthropogenic fire ignitions, the simulated trends in fire activity agree reasonably well with continental-scale reconstructions from charcoal records, with the exception of Europe. For some regions the change in fire activity is predominantly controlled through changes in fuel availability (Australia monsoon, Central America tropics/subtropics). For other regions changes in fuel moisture are more important for the overall trend in fire activity (North America, Sub-Saharan Africa, Europe, Asia monsoon). In Sub-Saharan Africa, for example, changes in fuel moisture alone lead to an increase in fire activity between 8000 and 200 cal yr BP, while changes in fuel availability lead to a decrease. Overall, the fuel moisture control is dominating the simulated fire activity for Sub-Saharan Africa. The simulations clearly demonstrate that both changes in fuel availability and changes in fuel moisture are important drivers for the fire activity over the Holocene. Fuel availability and fuel moisture do, however, have different climate controls. As such, observed changes in fire activity cannot be related to single climate parameters such as precipitation or temperature alone. Fire models, as applied in this study, in combination with observational records can help in understanding the climate control on fire activity, which is essential to project future fire activity.

Description: Shifting momentum balance and frictional adjustment observed over the inner-shelf during a storm Ocean Science Discussions, 12, 897-924, 2015 Author(s): M. Grifoll, A. Aretxabaleta, J. L. Pelegrí, and M. Espino We investigate the rapidly changing equilibrium between the momentum sources and sinks during the passage of a two-peak storm over the Catalan inner-shelf (NW Mediterranean Sea). Velocity measurements at 24 m water depth are taken as representative of the inner shelf, and the cross-shelf variability is explored with additional measurements at 50 m water depth. At 24 m, as the storm-related wind stress accelerated the flow, velocity increased throughout the water column, resulting in bottom stress starting to become important. The sea level also responded, with the pressure gradient force opposing the wind stress. In particular, during the second wind pulse, there were rapid oscillations in the acceleration and advective terms, apparently reflecting the incapacity of the bottom stress to dissipate the high kinetic energy of the system. The Coriolis and wave induced terms (via radiation stresses) were less important in the momentum balance. The frictional adjustment time scale was around 10 h, consistent with the e-folding time obtained from bottom drag parameterizations. Estimates of the frictional time and Ekman depth confirm the prevailing frictional response at 24 m. The momentum evolution in deeper parts of the shelf (50 m) showed an increase in the Coriolis force at the expense of the frictional term, typical in the transition from the inner to the mid-shelf.

Description: Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements Ocean Science Discussions, 12, 1051-1082, 2015 Author(s): Ø. Kleiv, A. Folkestad, J. Høkedal, K. Sørensen, and E. Aas During four field days in the years 2009–2011, 22 series of measurement were collected in the Inner Oslofjord. The data consist of recordings of spectral sub-surface and above-surface nadir radiances, as well as spectral downward irradiance in air. The studied wavelengths are 351, 400 nm and the 10 former MERIS channels in the range 413–754 nm. The water-leaving radiance and the reflected radiance at the sea surface can be determined from the measured nadir radiances in water and air. A simpler and much faster method, which determines the radiance reflectance at the surface as well as the water-leaving and reflected radiances solely from the measurements of upward nadir radiance and downward irradiance in air, is presented. A comparison between the quantities determined by the two methods shows that the average relative deviations between their results are less than or equal to 15% for the reflected radiance, at the studied wavelengths. The average relative deviations of the water-leaving radiance at 560 nm is 24%. We consider this to be acceptable uncertainties for a first check of satellite products in coastal waters.

Description: Boreal fire records in Northern Hemisphere ice cores: A review Michel Legrand, Joseph McConnell, Hubertus Fischer, Eric W. Wolff, Susanne Preunkert, Nathan Chellman, Daiana Leuenberger, Olivia Maselli, Michael Sigl, Simon Schüpbach, and Mike Flannigan Clim. Past Discuss., doi:10.5194/cp-2016-70,2016 Manuscript under review for CP (discussion: open, 0 comments) Here we review previous attempts made to reconstruct past forest fire using chemical signals recorded in Greenland ice. We showed that the Greenland ice records of ammonium, found to be a good fire proxy, consistently indicate changing fire activity in Canada in response to past climatic conditions that occurred since the last 15 000 years including the little ice age and the last large climatic transition.

Description: Palynological evidence for late Miocene stepwise aridification on the northeastern Tibetan Plateau Jia Liu, Ji Jun Li, Chun Hui Song, Hao Yu, Ting Jiang Peng, Zheng Chuang Hui, and Xi Yan Ye Clim. Past, 12, 1473-1484, doi:10.5194/cp-12-1473-2016, 2016 The late Cenozoic basins in the northeastern Tibetan Plateau document both the tectonic uplift process and its associated environmental changes. Here, we investigated a late Miocene sporopollen record from the Tianshui Basin in the northeastern Tibetan Plateau. The results show that a persistent aridification trend parallels the global cooling of the late Miocene, and the stepwise vegetation succession is consistent with the major uplift events of the Tibetan Plateau.

Description: First year of the new Arctic AWIPEV-COSYNA cabled Underwater Observatory in Kongsfjorden, Spitsbergen Philipp Fischer, Max Schwanitz, Reiner Loth, Uwe Posner, Markus Brand, and Friedhelm Schröder Ocean Sci. Discuss., doi:10.5194/os-2016-52,2016 Manuscript under review for OS (discussion: open, 0 comments) We observed oceanographic and community data from October 2013 to November 2014 in the shallow waters of Kongsfjorden on the west coast of Svalbard (Norway) using remote controlled hydrographic and optic sensors. Daily vertical profiles of temperature, salinity and turbidity were sampled together with stereo images of the macrobiotic community, including fish. A distinct seasonal cycle in total species abundances was found with surprisingly high animal counts during the polar winter.

Description: Holocene hydrological changes in the Rhône River (NW Mediterranean) as recorded in the marine mud belt Maria-Angela Bassetti, Serge Berné, Marie-Alexandrine Sicre, Bernard Dennielou, Yoann Alonso, Roselyne Buscail, Bassem Jalali, Bertil Hebert, and Christophe Menniti Clim. Past, 12, 1539-1553, doi:10.5194/cp-12-1539-2016, 2016 This work represents the first attempt to decipher the linkages between rapid climate changes and continental Holocene paleohydrology in the NW Mediterranean shallow marine setting. Between 11 and 4 ka cal BP, terrigenous input increased and reached a maximum at 7 ka cal BP, probably as a result of a humid phase. From ca. 4 ka cal BP to the present, enhanced variability in the land-derived material is possibly due to large-scale atmospheric circulation and rainfall patterns in western Europe.

Description: Regional climate signal vs. local noise: a two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land Thomas Münch, Sepp Kipfstuhl, Johannes Freitag, Hanno Meyer, and Thomas Laepple Clim. Past, 12, 1565-1581, doi:10.5194/cp-12-1565-2016, 2016 Ice-core oxygen isotope ratios are a key climate archive to infer past temperatures, an interpretation however complicated by non-climatic noise. Based on 50 m firn trenches, we present for the first time a two-dimensional view (vertical × horizontal) of how oxygen isotopes are stored in Antarctic firn. A statistical noise model allows inferences for the validity of ice coring efforts to reconstruct past temperatures, highlighting the need of replicate cores for Holocene climate reconstructions.

Description: Comparison of the simulated upper-ocean vertical structure using 1-dimensional mixed-layer models Sonaljit Mukherjee and Amit Tandon Ocean Sci. Discuss., doi:10.5194/os-2016-45,2016 Manuscript under review for OS (discussion: open, 0 comments) Atmospheric fluxes influence the momentum and scalar properties in the upper-cean. Buoyancy fluxes result in a diurnal variability in the sea-surface temperature (SST), whereas the wind stress forms near-inertial currents in the mixed layer (ML). In this study, we investigate the contrasts between the simulated SST and the vertical structure of the temperature and shear by three different mixing models: the PWP bulk mixed-layer model, the KPP non-local boundary layer model and the κ−ϵ local mixing model. We choose two upper-ocean datasets for our studies, namely the SWAPP (1990) and the MLML (1991). The SWAPP dataset shows the presence of strong near-inertial shear below the ML and negligible near-inertial shear within the ML. The MLML dataset shows a negligible rise in the SST during the first 22 day mixing phase, which is followed by a steep rise by 6 °C during the subsequent 75 day restratification phase. Comparison with the SWAPP dataset shows that the KPP and κ−ϵ models form strong shear near the surface due to weak eddy viscosities, thus producing a thin shear layer over the entire range of frequencies in the wind stress. At the ML base, the models form an inertial and a diurnal maximum. The inertial maximum extends over a substantial range of depths, and is continuous for the κ−ϵ model but discontinuous for the KPP and PWP models. Comparison with the MLML dataset reveals that the KPP yields the largest SST amplitude over a 24-hour diurnal cycle, and is followed by the κ−ϵ and PWP. However, the net warming of SST at the end of the diurnal cycle is stronger for the PWP compared to κ−ϵ and KPP. The PWP also forms stronger temperature gradients at the ML base compared to κ−ϵ and KPP. Over multiple diurnal cycles, the shallowing and deepening of the mixed layer results in multiple sharp temperature gradients in PWP, thus forming a serrated vertical profile that remains unaffected during the restratification phase of the MLML dataset.

Description: Aragonite saturation states and pH in western Norwegian fjords: seasonal cycles and controlling factors, 2005–2009 Abdirahman M. Omar, Ingunn Skjelvan, Svein Rune Erga, and Are Olsen Ocean Sci., 12, 937-951, doi:10.5194/os-12-937-2016, 2016 We have determined, for the first time, the seasonal changes and controlling processes of ocean acidification parameters across western Norwegian fjords, based on data obtained mainly with sensors on board a commercial ship, MS Trans Carrier , in 2005–2009. The study fills an important gap in our knowledge on ocean acidification in western Norwegian fjords, which are important ecosystems: important recreation areas, marine pathways, spawning grounds for different fish species, etc.

Description: Observed and simulated full-depth ocean heat-content changes for 1970–2005 Lijing Cheng, Kevin E. Trenberth, Matthew D. Palmer, Jiang Zhu, and John P. Abraham Ocean Sci., 12, 925-935, doi:10.5194/os-12-925-2016, 2016 A new method of observing ocean heat content throughout the entire ocean depth is provided. The new method is compared with simulated ocean heat content changes from climate models. The comparisons are carried out in various depth layers of the ocean waters. It is found that there is excellent agreement between the models and the observations. Furthermore, we propose that changes to ocean heat content be used as a fundamental metric to evaluate climate models.

Description: Accessing diverse data comprehensively – CODM, the COSYNA data portal Gisbert Breitbach, Hajo Krasemann, Daniel Behr, Steffen Beringer, Uwe Lange, Nhan Vo, and Friedhelm Schroeder Ocean Sci., 12, 909-923, doi:10.5194/os-12-909-2016, 2016 The coastal observation system COSYNA aims to describe the physical and biogeochemical state of a regional coastal system. The COSYNA data management (CODM) is the link between observations, model results and data usage. The challenge for CODM is the integration of diverse data sources in terms of parameters, dimensionality and observation methods to gain a comprehensive view of the observations. How this is achieved is described in the paper.

Description: An improved North-South synchronization of ice core records around the 41 K beryllium 10 peak G. M. Raisbeck, A. Cauquoin, J. Jouzel, A. Landais, J.-R. Petit, V. Y. Lipenkov, J. Beer, H.-A. Synal, H. Oerter, S. J. Johnsen, J. P. Steffensen, A. Svensson, and F. Yiou Clim. Past Discuss., doi:10.5194/cp-2016-79,2016 Manuscript under review for CP (discussion: open, 0 comments) Using records of a long lived radioactive nuclide ( 10 Be) that is formed globally in the atmosphere and deposited within a few years to the earth's surface, we have synchronized 3 Antarctic ice cores to one from Greenland. This permits the climate and other environmental parameters registered in these ice cores to be put on a common time scale with a precision of a few decades, thus allowing different models and mechanisms associated with these parameters to be tested with the same precision.

Description: Freshening of Antarctic Intermediate Water in the South Atlantic Ocean in 2005–2014 Wenjun Yao and Jiuxin Shi Ocean Sci. Discuss., doi:10.5194/os-2016-54,2016 Manuscript under review for OS (discussion: open, 0 comments) Antarctic Intermediate Water (AAIW) in the South Atlantic Ocean has experienced basin-scaled freshening from 2005 to 2014, reflected by the Argo gridded products. Two zonal sections of WOCE observation also revealed a similar quasi-decadal signal. Our analysis revealed that such freshening was induced by the contemporaneous freshwater input in the AAIW ventilation region and the reduced more saline water carried by Agulhas Leakage.

Description: Changes in extreme regional sea level under global warming S.-E. Brunnabend, H. A. Dijkstra, M. A. Kliphuis, H. E. Bal, F. Seinstra, B. van Werkhoven, J. Maassen, and M. van Meersbergen Ocean Sci. Discuss., doi:10.5194/os-2016-57,2016 Manuscript under review for OS (discussion: open, 0 comments) An important contribution to future changes in regional sea level extremes is due to the changes in intrinsic ocean variability, in particular ocean eddies. Here, we study a scenario of future dynamic sea level (DSL) extremes using a strongly eddying version of the Parallel Ocean Program. Changes in 10-year return time DSL extremes are very inhomogeneous over the globe and are related to changes in ocean currents and corresponding regional shifts in ocean eddy pathways.

Description: Freshening of the Labrador Sea as a trigger for Little Ice Age development Montserrat Alonso-Garcia, Helga F. Kleiven, Jerry F. McManus, Paola Moffa-Sanchez, Wallace Broecker, and Benjamin P. Flower Clim. Past Discuss., doi:10.5194/cp-2016-80,2016 Manuscript under review for CP (discussion: open, 0 comments) This study focuses on understanding climatic and oceanographic variations that took place during the last 1000 years. We studied sediment samples from the Labrador Sea looking for evidence of events of freshwater and iceberg discharges to this region. The importance of this study is to evaluate when these events happened and its possible consequences. The freshening of the Labrador Sea region may have played a major role on the cooling underwent during the 15th to 19th centuries.

Description: The role of basal hydrology in the surging of the Laurentide Ice Sheet William H. G. Roberts, Antony J. Payne, and Paul J. Valdes Clim. Past, 12, 1601-1617, doi:10.5194/cp-12-1601-2016, 2016 There are observations from ocean sediment cores that during the last ice age the Laurentide Ice Sheet, which sat over North America, periodically surged. In this study we show the role that water at the base of an ice sheet plays in these surges. We show that with a more realistic representation of water drainage at the base of the ice sheet than usually used, these surges can still occur and that they are triggered by an internal ice sheet instability; no external trigger is needed.

Description: A stable Faroe Bank Channel overflow 1995–2015 Bogi Hansen, Karin Margretha Húsgarð Larsen, Hjálmar Hátún, and Svein Østerhus Ocean Sci. Discuss., doi:10.5194/os-2016-56,2016 Manuscript under review for OS (discussion: open, 0 comments) The Faroe Bank Channel is one of the main passages for the flow of cold dense water from the Arctic into the depths of the World Ocean where it feeds the deep branch of the AMOC transporting heat and carbon dioxide from the atmosphere into the deep ocean. Based on in situ measurements we show that the volume transport of this flow has been stable from 1995 to 2015. The water has warmed, but has not become less dense. Thus, this branch of the AMOC did not weaken during the last two decades.

Description: North American regional climate reconstruction from Ground Surface Temperature Histories Fernando Jaume-Santero, Carolyne Pickler, Hugo Beltrami, and Jean-Claude Mareschal Clim. Past Discuss., doi:10.5194/cp-2016-85,2016 Manuscript under review for CP (discussion: open, 0 comments) Within the framework of the PAGES NAm2k project, we estimated regional trends in the ground surface temperature change for the past 500 years in North America. The mean North American ground surface temperature history suggests a warming of 1.8 °C between preindustrial times and 2000. A regional analysis of mean temperature changes over the last 5 centuries shows that all regions experienced warming, but this warming displays large spatial variability, and is more marked in high latitude regions.

Description: The 1816 ‘year without a summer’ in an atmospheric reanalysis Philip Brohan, Gilbert P. Compo, Stefan Brönnimann, Robert J. Allan, Renate Auchmann, Yuri Brugnara, Prashant D. Sardeshmukh, and Jeffrey S. Whitaker Clim. Past Discuss., doi:10.5194/cp-2016-78,2016 Manuscript under review for CP (discussion: open, 0 comments) We have used modern weather forecasting tools to reconstruct the dreadful European weather of 200 years ago – 1816 was the ‘year without a summer’; harvests failed, and people starved. We can show that 1816’s extreme climate was caused by the eruption of the Tambora volcano the previous year. This means we have some chance of predicting such extreme summers if they occur in future, though this is still a challenge to today’s forecast models.

Description: GEM: A Dynamic Tracking Model for Mesoscale Eddies in the Ocean Qiu-Yang Li, Liang Sun, and Sheng-Fu Lin Ocean Sci. Discuss., doi:10.5194/os-2016-49,2016 Manuscript under review for OS (discussion: open, 0 comments) Genealogical Evolution Model (GEM) is an efficient logical model used to track dynamic evolution of mesoscale eddies in the ocean. It can distinguish different dynamic processes (e.g., merging and splitting) within a dynamic evolution pattern with a two-dimensional vector. All of the computational steps are linear and do not include iteration. It is very fast and is potentially useful for studying dynamic processes in other related fields, e.g., the dynamics of cyclones in meteorology.

Description: North Atlantic Oscillation controls on oxygen and hydrogen isotope gradients in winter precipitation across Europe; implications for palaeoclimate studies Michael Deininger, Martin Werner, and Frank McDermott Clim. Past Discuss., doi:10.5194/cp-2016-77,2016 Manuscript under review for CP (discussion: open, 0 comments) This study investigates the NAO-related mechanisms that control winter-precipitation stable oxygen and hydrogen isotope gradients across Europe. The results show that past longitudinal stable oxygen and hydrogen isotope gradients in European rainfall stored in palaeoclimate archives (e.g. speleothems) can be used to infer the past winter NAO modes from its variations.

Description: Influence of proxy data uncertainty on data assimilation for the past climate Anastasios Matsikaris, Martin Widmann, and Johann Jungclaus Clim. Past, 12, 1555-1563, doi:10.5194/cp-12-1555-2016, 2016 We have assimilated proxy-based (PAGES 2K) and instrumental (HadCRUT3v) observations into a General Circulation Model (MPI-ESM-CR). Assimilating instrumental data improves the performance of Data Assimilation. No skill on small spatial scales is however found for either of the two schemes. Errors in the assimilated data are therefore not the main reason for this lack of skill; continental mean temperatures cannot provide skill on small spatial scales in palaeoclimate reconstructions.

Description: Quantification of southwest China rainfall during the 8.2 ka BP event with response to North Atlantic cooling Yuhui Liu and Chaoyong Hu Clim. Past, 12, 1583-1590, doi:10.5194/cp-12-1583-2016, 2016 The 8.2 ka BP event, a global climate anomaly that occurred 8200 years ago, could provide climate teleconnection information for the simulation of abrupt climate changes, but there are few quantitative reconstructions of this event. This paper provides a 10-year resolution rainfall record from the East Asian monsoon area during the event, showing the reduced rainfall in southwest China during the 8.2 ka BP period was coupled with Greenland cooling with a possible response rate of 110 ± 30 mm/℃.

Description: Could the Pliocene constrain the equilibrium climate sensitivity? J. C. Hargreaves and J. D. Annan Clim. Past, 12, 1591-1599, doi:10.5194/cp-12-1591-2016, 2016 The mid-Pliocene Warm Period, 3 million years ago, was the most recent interval with high greenhouse gases. By modelling the period with the same models used for future projections, we can link the past and future climates. Here we use data from the mid-Pliocene to produce a tentative result for equilibrium climate sensitivity. We show that there are considerable uncertainties that strongly influence the result, but we are optimistic that these may be reduced in the next few years.

Description: Sub-basin scale sea level budgets from satellite altimetry, Argo floats and satellite gravimetry in the North Atlantic Marcel Kleinherenbrink, Riccardo Riva, and Yu Sun Ocean Sci. Discuss., doi:10.5194/os-2016-50,2016 Manuscript under review for OS (discussion: open, 0 comments) Satellite altimetry measures changes in sea level, while satellite gravimetry measures mass changes and from Argo temperature and salinity profiles one can infer steric sea level. For the first time it is shown that the mass and steric components match in most cases the total sea level measured by altimetry on a sub-basin scale in terms of trend, annual amplitude and interannual variability. We also find that the choice of gravity field filter is essential to close the budget.

Description: Technical note: GODESS – a profiling mooring in the Gotland Basin Ralf D. Prien and Detlef E. Schulz-Bull Ocean Sci., 12, 899-907, doi:10.5194/os-12-899-2016, 2016 A profiling mooring with an interdisciplinary suite of sensors for water depths up to 300 m is described in this note. It can be programmed to take profiles through the water column at set times or intervals and with the standard set of batteries is able to profile about 34 km in total (e.g. 200 profiles of 170 m profiling each). The mooring was designed to observe the dynamics of the redoxcline in the Gotland Basin over periods of up to 3 months.

Description: Multi-timescale data assimilation for atmosphere–ocean state estimates Nathan Steiger and Gregory Hakim Clim. Past, 12, 1375-1388, doi:10.5194/cp-12-1375-2016, 2016 We present a data assimilation algorithm that incorporates proxy data at arbitrary timescales. Within a synthetic-test framework, we find that atmosphere–ocean states are most skillfully reconstructed by incorporating proxies across multiple timescales compared to using them at short or long timescales alone. Additionally, reconstructions that incorporate long-timescale proxies improve the low-frequency components of the reconstructions relative to using only high-resolution proxies.

Description: Holocene biome changes in Asia – an analysis of different transient Earth system model simulations Anne Dallmeyer, Martin Claussen, Jian Ni, Xianyong Cao, Yongbo Wang, Nils Fischer, Madlen Pfeiffer, Liya Jin, Vyacheslav Khon, Sebastian Wagner, Kerstin Haberkorn, and Ulrike Herzschuh Clim. Past Discuss., doi:10.5194/cp-2016-67,2016 Manuscript under review for CP (discussion: open, 0 comments) The vegetation distribution in Eastern Asia is supposed to be very sensitive to climate change. Since proxy records are scarce, hitherto a mechanistic understanding of the past spatio-temporal climate-vegetation relationship is lacking. To assess the Holocene vegetation change, we forced the diagnostic biome model BIOME4 with climate anomalies of different transient climate simulations.

Description: Evaluation of Peaks-Over-Threshold Method Soheil Saeed Far and Ahmad Khairi Abd. Wahab Ocean Sci. Discuss., doi:10.5194/os-2016-47,2016 Manuscript under review for OS (discussion: open, 0 comments) In this paper, two commonly used extreme value analysis models have been developed (POT and GPD models). Both models use threshold values to censor a range of data. The results of this study show the two models are very sensitive to any changes in threshold value. Moreover, the POT model has shown some imperfections in determining true threshold value and a best fitting distribution function. Two methods were proposed by this paper to deal with the limitations in order to improve the model.

Description: Seiche excitation in a highly stratified fjord of southern Chile: the Reloncaví fjord Manuel I. Castillo, Oscar Pizarro, Nadin Ramirez, and Mario Caceres Ocean Sci. Discuss., doi:10.5194/os-2016-42,2016 Manuscript under review for OS (discussion: open, 0 comments) Here we present the results of an intensive physical oceanography study on the Reloncavi fjord (41.5º S, 72.5º W) focused on the subinertial time-scale. The along-fjord currents presented 3 days oscillations which were consistent with the natural internal period of oscillation of the fjord basin (internal seiche). This oscillation could exexplain more than 44 % of the 3 days variability and contributed levels of kinetic energy as large as the tidal currents.

Description: Marine mammal tracks from two-hydrophone acoustic recordings made with a glider Elizabeth T. Küsel, Tessa Munoz, Martin Siderius, David K. Mellinger, and Sara Heimlich Ocean Sci. Discuss., doi:10.5194/os-2016-48,2016 Manuscript under review for OS (discussion: open, 0 comments) An ocean glider was tested during the REP14-MED experiment off the western coast of the Island of Sardinia as a platform for recording sounds produced by whales and dolphins using two sensors. Sperm whale clicks as well as dolphin clicks and whistles were identified in the recordings. Automatically detected sperm whale clicks were used to estimate animal tracks. Such information is useful for marine mammal density estimation studies that use passive acoustics.

Description: Glacial δ 13 C decreases in the western South Atlantic forced by millennial changes in Southern Ocean ventilation Marília C. Campos, Cristiano M. Chiessi, Ines Voigt, Alberto R. Piola, Henning Kuhnert, and Stefan Mulitza Clim. Past Discuss., doi:10.5194/cp-2016-59,2016 Manuscript under review for CP (discussion: open, 0 comments) Abrupt climate change events of the last deglaciation were accompanied by increases in atmospheric CO 2 presumably originated by outgassing from the Southern Ocean. We present new planktonic foraminiferal stable carbon isotopic data from the western South Atlantic that suggest that the CO 2 added to the atmosphere during abrupt climate change events of the last glacial period also originated in the ocean and reached the atmosphere by outgassing from the Southern Ocean.

Description: Jens Esmark's Christiania (Oslo) meteorological observations 1816–1838: The first long term continuous temperature record from the Norwegian capital homogenized and analysed Geir Hestmark and Øyvind Nordli Clim. Past Discuss., doi:10.5194/cp-2016-60,2016 Manuscript under review for CP (discussion: open, 0 comments) The detailed and continuous meteorological observations of professor Jens Esmark from the capital of Norway in the period 1816 to 1838 are evaluated, homogenized and reanalyzed with modern methods to characterize the weather in Oslo in this period.

Description: The importance of external climate forcing for the variability and trends of coastal upwelling in past and future climate Nele Tim, Eduardo Zorita, Birgit Hünicke, Xing Yi, and Kay-Christian Emeis Ocean Sci., 12, 807-823, doi:10.5194/os-12-807-2016, 2016 The impact of external climate forcing on the four eastern boundary upwelling systems is investigated for the recent past and future. Under increased radiative forcing, upwelling-favourable winds should strengthen due to unequal heating of land and oceans. However, coastal upwelling simulated in ensembles of climate simulations do not show any imprint of external forcing neither for the past millennium nor for the future, with the exception of the strongest future scenario.

Description: Seasonal, Spring-Neap and Tidal Variation of Hydrodynamics and Water Constituents in the Mouth of the Elbe Estuary, Germany Jens Kappenberg, Michael Berendt, Nino Ohle, Rolf Riethmüller, Dagmar Schuster, and Thomas Strotmann Ocean Sci. Discuss., doi:10.5194/os-2016-7,2016 Manuscript under review for OS (discussion: open, 0 comments) Results of long-term measurements of CTD, current velocity, turbidity, and dissolved oxygen from three stations in the mouth of the Elbe Estuary in northern Germany are presented for the period of 2012 and 2013. The focus is on a station named HPA-Elbe 1, which is part of the COSYNA coastal observing system for northern and arctic seas, but data from two neighbouring stations are also presented for comparison and to bridge gaps in the time-series of HPA-Elbe 1. The variations of the variables exhibit distinct tidal patterns related to the longitudinal estuarine gradients of the water constituents and local sediment dynamics. On longer time-scales, spring-neap variability is observed, most prominently in the hydrodynamics. On the seasonal scale, the water temperature influences the degradation processes, which deplete the dissolved oxygen on the one hand and increase the oxygen contents by biological respiration on the other hand. Freshwater events from the catchment play an important role for sediment dynamics and mixing of riverine and coastal waters in the brackish water reach of the estuary. The periods of the deployment of the stations comprise the severest river flood observed so far in the Elbe in June 2013. The effects of the flood at the stations and along the estuary consist of a rapid flushing of the mixing zone and the turbidity maximum to the outer estuary and the transition to freshwater conditions from Hamburg to the mouth at Cuxhaven. The impact of the river flood at the stations is more pronounced in changes in salinity than in turbidity. The restoration of estuarine salinity and turbidity values comparable to those before the river flood took several months.

Description: Large-scale drivers of Caucasus climate variability in meteorological records and Mt Elbrus ice cores Anna Kozachek, Vladimir Mikhalenko, Valérie Masson-Delmotte, Alexey Ekaykin, Patrick Ginot, Stanislav Kutuzov, Michel Legrand, Vladimir Lipenkov, and Susanne Preunkert Clim. Past Discuss., doi:10.5194/cp-2016-62,2016 Manuscript under review for CP (discussion: open, 0 comments) A 181.2 m ice core was recovered from a borehole drilled into bedrock on the western plateau of Mt. Elbrus (43°20’53.9’’ N, 42°25’36.0’’ E; 5115 m a.s.l.) in the Caucasus, Russia, in 2009 (Mikhalenko et al., 2015). Here, we report on the results of the water stable isotope composition from this ice core in comparison with results from shallow ice cores. There is a distinct seasonal cycle of the isotopic composition which allowed dating by annual layer counting. Dating has been performed for the upper 126 m of the deep core combined with shallow cores data. The whole record covers one century from 2013 back to 1914. Due to the high accumulation rate (1380 mm w.e. per year) and limited melting we obtained the isotopic composition and accumulation rate records with seasonal resolution. These values were compared with available meteorological data from 13 weather stations in the region, and also with atmosphere circulation indices, back-trajectories calculations and GNIP data in order to decipher the drivers of accumulation and ice core isotopic composition in the Caucasus region. In the summer season the isotopic composition depends on the local temperature, while in winter, the atmospheric circulation is the predominant driver of the ice core isotopic composition. The snow accumulation rate correlates well with the precipitation rate in the region all year round, this made it possible to reconstruct and expand the precipitation record at the Caucasus highlands from 1914 till 1966 when the reliable meteorological observations of precipitation at high elevation began.

Description: Hydrological variations of the intermediate water masses of the western Mediterranean Sea during the past 20 ka inferred from neodymium isotopic composition in foraminifera and cold-water corals Quentin Dubois-Dauphin, Paolo Montagna, Giuseppe Siani, Eric Douville, Claudia Wienberg, Dierk Hebbeln, Zhifei Liu, Nejib Kallel, Arnaud Dapoigny, Marie Revel, Edwige Pons-Branchu, and Christophe Colin Clim. Past Discuss., doi:10.5194/cp-2016-64,2016 Manuscript under review for CP (discussion: open, 0 comments) The neodymium isotopic composition (εNd) of mixed planktonic foraminifera species and scleractinian cold-water corals (CWC; Madrepora oculata , Lophelia pertusa ) collected at 280–620 m water depth in the Balearic Sea, the Alboran Sea and the south Sardinian continental margin was investigated to constrain hydrological variations at intermediate depths in the western Mediterranean Sea during the last 20 ka. Planktonic ( Globigerina bulloides ) and benthic ( Cibicidoides pachyderma ) foraminifera were also analyzed for stable oxygen (δ 18 O) and carbon (δ 13 C) isotopes. The foraminiferal and coral εNd values from the Balearic Sea and the Alboran Sea are comparable over the past ~ 13 ka, with mean values of −8.94 ± 0.26 (1σ; n = 24) and −8.91 ± 0.18 (1σ; n = 25), respectively. Before 13 ka BP, the foraminiferal εNd values are slightly lower (−9.28 ± 0.15) and tend to reflect a higher mixing between intermediate and deep waters, characterized by more unradiogenic εNd values. The slight εNd increase after 13 ka BP is associated to a marked difference in the benthic foraminiferal δ 13 C composition of intermediate and deeper depths, which started at ~ 16 ka BP. This suggests an earlier stratification of the water masses and a subsequent reduced contribution of unradiogenic εNd from deep waters. The CWC from the Sardinia Channel show a much larger scattering of εNd values, from −8.66 ± 0.30 to −5.99 ± 0.50, and a lower average (−7.31 ± 0.73; n = 19) compared to the CWC and foraminifera from the Alboran Sea and Balearic Sea, indicative of intermediate waters sourced from the Levantine basin. At the time of sapropel S1 deposition (10.2 to 6.4 ka), the εNd values of the Sardinian CWC become more unradiogenic (−8.38 ± 0.47; n = 3 at ~ 8.7 ka BP), suggesting a significant contribution of intermediate waters originated from the western basin. Accordingly, we propose here that western Mediterranean intermediate waters replaced the Levantine Intermediate Water (LIW), which was strongly reduced during the mid-sapropel (~ 8.7 ka BP). This observation supports a notable change of Mediterranean circulation pattern centered on sapropel S1 that needs further investigations to be confirmed.

Description: Climatic effects and impacts of the 1815 eruption of Mount Tambora in the Czech Lands Rudolf Brázdil, Ladislava Řezníčková, Hubert Valášek, Lukáš Dolák, and Oldřich Kotyza Clim. Past, 12, 1361-1374, doi:10.5194/cp-12-1361-2016, 2016 The paper deals with climatic and human impacts of the strong Tambora (Indonesia) volcanic eruption in April 1815 over the Czech Lands territory based on analysis of documentary data and instrumental records. While climatic effects were related particularly to summers 1815 and 1816 (1816 is known as "a Year Without Summer"), quite important were societal impacts represented after bad harvest by steep increase in prices and shortages of food.

Description: Sensitivity of Pliocene climate simulations in MRI-CGCM2.3 to respective boundary conditions Youichi Kamae, Kohei Yoshida, and Hiroaki Ueda Clim. Past Discuss., doi:10.5194/cp-2016-50,2016 Manuscript under review for CP (discussion: open, 0 comments) Climate model simulations conducted in previous studies tended to underestimate higher-latitude warming during the late Pliocene suggested by proxy evidences. We explore how prescribed trace gases, ice sheet, vegetation, lakes and orography affect the Pliocene climate simulation based on a protocol of the PlioMIP Phase 2. The revised boundary forcing data lead to amplified higher-latitude warming that is qualitatively consistent with the paleoenvironment reconstructions.

Description: Ocean Forecasting: From Regional to Coastal Scales Emil V. Stanev, Johannes Schulz-Stellenfleth, Joanna Staneva, Sebastian Grayek, Sebastian Grashorn, Arno Behrens, Wolfgang Koch, and Johannes Pein Ocean Sci. Discuss., doi:10.5194/os-2016-25,2016 Manuscript under review for OS (discussion: open, 0 comments) This paper describes coastal ocean forecasting practices exemplified for the North and Baltic Sea. It identifies new challenges, most of which are associated with the non-linear behavior of coastal ocean. It describes assimilation of remote sensing, in situ and HF radar data, prediction of wind waves and storm surges, as well as possible applications to search and rescue operations, and modelling support for assessing the environmental impact of wind parks. Concepts for seamless approaches to li

Description: Effects of melting ice sheets and orbital forcing on the early Holocene warming in the extratropical Northern Hemisphere Yurui Zhang, Hans Renssen, and Heikki Seppä Clim. Past, 12, 1119-1135, doi:10.5194/cp-12-1119-2016, 2016 We explore how forcings contributed to climate change during the early Holocene that marked the final transition to the warm and stable stage. Our results indicate that 1) temperature at the Holocene onset was lower than in the preindustrial over the northern extratropics with the exception in Alaska, and the magnitude of this cooling varies regionally as a response to varying climate forcings and diverse mechanisms, and 2) the rate of the early Holocene warming was also spatially heterogeneous.

Description: A possibility of large scale intrusions generation in the Arctic Ocean under stable-stable stratification: an analytical consideration Natalia Kuzmina Ocean Sci. Discuss., doi:10.5194/os-2016-15,2016 Manuscript under review for OS (discussion: open, 0 comments) Some analytical solutions are found for the problem of three-dimensional instability of a weak geostrophic flow with linear velocity shear taking into account vertical diffusion of buoyancy. The analysis is based on the potential vorticity equation in a long-wave approximation when the horizontal scale of disturbances is taken to be much larger than the local baroclinic Rossby radius. It is hypothesized that the solutions found can be applied to describe stable and unstable disturbances on a planetary scale with respect, especially, to the Arctic Basin, where weak baroclinic fronts with typical temporal variability periods of the order of several years or more are observed and the beta-effect is negligible. Stable (decaying with time) solutions describe disturbances that, in contrast to the Rossby waves, can propagate to both the west and east, depending on the sign of the linear shear of geostrophic velocity. The unstable (growing with time) solutions are applied to describe large-scale intrusions at baroclinic fronts under the stable–stable thermohaline stratification observed in the upper layer of the Polar Deep Water in the Eurasian Basin. The proposed description of intrusive layering can be considered as a possible alternative to the mechanism of interleaving due to the differential mixing.

Description: Sea ice and pollution-modulated changes in Greenland ice core methanesulfonate and bromine O. J. Maselli, N. J. Chellman, M. Grieman, L. Layman, J. R. McConnell, D. Pasteris, R. H. Rhodes, E. Saltzman, and M. Sigl Clim. Past Discuss., doi:10.5194/cp-2016-49,2016 Manuscript under review for CP (discussion: open, 0 comments) We analyzed two Greenland ice cores for methanesulfonate (MSA) and bromine (Br) and concluded that both species are suitable proxies for local sea ice conditions. Interpretation of the records reveals that there have been sharp declines in sea ice in these areas in the past 250 years. However, at both sites the Br record deviates from MSA during the industrial period, raising questions about the value of Br as a sea ice proxy during recent periods of high, industrial atmospheric acid pollution.

Description: Spatial climate dynamics in the Iberian Peninsula since 15 000 yr BP Pedro Tarroso, José Carrión, Miriam Dorado-Valiño, Paula Queiroz, Luisa Santos, Ana Valdeolmillos-Rodríguez, Paulo Célio Alves, José Carlos Brito, and Rachid Cheddadi Clim. Past, 12, 1137-1149, doi:10.5194/cp-12-1137-2016, 2016 The climate fluctuates between warm and cold stages, forcing biodiversity to shift patterns according to climatic tolerance. Here we provide an analysis of the shifting patterns of climate in the Iberian Peninsula for the last 15 000 years. By analysing climate in the spatial and temporal dimensions, we were able to divide the peninsula into areas that shared similar climate patterns and to derive a map of climate stability for this period.

Description: Sulphur-rich volcanic eruptions triggered extreme hydrological events in Europe since AD 1850 Cristina Di Salvo and Gianluca Sottili Clim. Past Discuss., doi:10.5194/cp-2016-53,2016 Manuscript under review for CP (discussion: open, 0 comments) In Europe, intensities of hydrological extreme events were influenced by volcanic SO 2 concentrations in the Northern Hemisphere. SO 2 -rich eruptions, similar to the Bárðarbunga 2014–15 eruption (Iceland), by affecting Ocean-atmosphere heat exchange, affected the intensity of the NAO with effects on rainfall and flood intensities. SO 2 effects, superimposed to climate change, could enhance frequencies and intensities of extreme events, thus increasing the natural risks in densely populated area.

Description: Current temporal asymmetry and the role of tides: Nan-Wan Bay vs. the Gulf of Elat Yosef Ashkenazy, Erick Fredj, Hezi Gildor, Gwo-Ching Gong, and Hung-Jen Lee Ocean Sci., 12, 733-742, doi:10.5194/os-12-733-2016, 2016 Nan-Wan Bay in Taiwan and the Gulf of Elat in Israel are two different coastal environments, and as such, their currents are expected to have different statistical properties. We find that in spite of these differences, the statistical properties of the surface currents are similar in both basins. Still, surface currents are temporally asymmetric in Nan-Wan but not in Elat; we attribute this difference to the strong tides that exist in Nan-Wan but not in Elat.

Description: A universal error source in past climate estimates derived from tree rings Juhani Rinne, Mikko Alestalo, and Jörg Franke Clim. Past Discuss., doi:10.5194/cp-2016-27,2016 Manuscript under review for CP (discussion: open, 0 comments) The climate reconstructions derived from tree rings tend to show erroneous long-term oscillations. The aim of our paper is to describe the phenomenon and to uncover its reasons. In order to derive formulae describing the long-term error, the dependence of the tree rings on the age is not used in the reconstruction. The erroneous oscillations turn out to be due to data paucities over the years. Accordingly, such long-term errors can be present in any tree ring analysis with such paucities.

Description: Arctic sea ice simulation in the PlioMIP ensemble Fergus W. Howell, Alan M. Haywood, Bette L. Otto-Bliesner, Fran Bragg, Wing-Le Chan, Mark A. Chandler, Camille Contoux, Youichi Kamae, Ayako Abe-Ouchi, Nan A. Rosenbloom, Christian Stepanek, and Zhongshi Zhang Clim. Past, 12, 749-767, doi:10.5194/cp-12-749-2016, 2016 Simulations of pre-industrial and mid-Pliocene Arctic sea ice by eight GCMs are analysed. Ensemble variability in sea ice extent is greater in the mid-Pliocene summer, when half of the models simulate sea-ice-free conditions. Weaker correlations are seen between sea ice extent and temperatures in the pre-industrial era compared to the mid-Pliocene. The need for more comprehensive sea ice proxy data is highlighted, in order to better compare model performances.

Description: Comparison of simulated and reconstructed variations in East African hydroclimate over the last millennium François Klein, Hugues Goosse, Nicholas E. Graham, and Dirk Verschuren Clim. Past, 12, 1499-1518, doi:10.5194/cp-12-1499-2016, 2016 This paper analyses global climate model simulations of long-term East African hydroclimate changes relative to proxy-based reconstructions over the last millennium. No common signal is found between model results and reconstructions as well as among the model time series, which suggests that simulated hydroclimate is mostly driven by internal variability rather than by common external forcing.

Description: A 368-year maximum temperature reconstruction based on tree-ring data in the northwestern Sichuan Plateau (NWSP), China Liangjun Zhu, Yuandong Zhang, Zongshan Li, Binde Guo, and Xiaochun Wang Clim. Past, 12, 1485-1498, doi:10.5194/cp-12-1485-2016, 2016 We present a 368-year late summer maximum temperature reconstruction based on spruce tree rings. It touches on the critical topic of climate reconstruction in the eastern edge of Tibetan Plateau and represents an extension and enhancement of climate records for this area. The Little Ice Age was well represented and 20th century warming was not obvious in this reconstruction. This temperature variation may be affected by global land–sea atmospheric circulation as well as solar and volcanic forcing.

Description: The PRISM4 (mid-Piacenzian) paleoenvironmental reconstruction Harry Dowsett, Aisling Dolan, David Rowley, Robert Moucha, Alessandro M. Forte, Jerry X. Mitrovica, Matthew Pound, Ulrich Salzmann, Marci Robinson, Mark Chandler, Kevin Foley, and Alan Haywood Clim. Past, 12, 1519-1538, doi:10.5194/cp-12-1519-2016, 2016 Past intervals in Earth history provide unique windows into conditions much different than those observed today. We investigated the paleoenvironments of a past warm interval (~ 3 million years ago). Our reconstruction includes data sets for surface temperature, vegetation, soils, lakes, ice sheets, topography, and bathymetry. These data are being used along with global climate models to expand our understanding of the climate system and to help us prepare for future changes.

Description: Sea ice-related halogen enrichment at Law Dome, coastal East Antarctica Paul Vallelonga, Niccolo Maffezzoli, Andrew D. Moy, Mark A. J. Curran, Tessa R. Vance, Ross Edwards, Gwyn Hughes, Emily Barker, Gunnar Spreen, Alfonso Saiz-Lopez, J. Pablo Corella, Carlos A. Cuevas, and Andrea Spolaor Clim. Past Discuss., doi:10.5194/cp-2016-74,2016 Manuscript under review for CP (discussion: open, 0 comments) We present a study of bromine, iodine and sodium in an ice core from Law Dome, in coastal East Antarctica. We find that bromine and iodine variability at Law Dome is correlated to changes in the area of sea ice along the Law Dome coast as observed by satellite since the early 1970s. These findings are in agreement with a previous study based on MSA and confirm a long-trem trend of sea ice decrease for this sector of Antarctica over the 20th century.

Description: Atmospheric methane control mechanisms during the early Holocene Ji-Woong Yang, Jinho Ahn, Edward J. Brook, and Yeongjun Ryu Clim. Past Discuss., doi:10.5194/cp-2016-75,2016 Manuscript under review for CP (discussion: open, 0 comments) The early Holocene climate is chracterized as an interglacial boundary condition without substantial human influence. Here we present a high-resolution CH 4 time series during the early Holocene for investigating a natural control process. The results show that changes in the ITCZ position and Asian summer monsoon intensity were able to induce ~ 20 to 40 ppb CH 4 variability in millennial time scale by changing low latitude emission, while the contribution of boreal sources increased gradually.

Description: Developing European operational oceanography for Blue Growth, climate change adaptation and mitigation, and ecosystem-based management Jun She, Icarus Allen, Erik Buch, Alessandro Crise, Johnny A. Johannessen, Pierre-Yves Le Traon, Urmas Lips, Glenn Nolan, Nadia Pinardi, Jan H. Reißmann, John Siddorn, Emil Stanev, and Henning Wehde Ocean Sci., 12, 953-976, doi:10.5194/os-12-953-2016, 2016 This white paper addresses key scientific challenges and research priorities for the development of operational oceanography in Europe for the next 5–10 years. Knowledge gaps and deficiencies are identified in relation to common scientific challenges in four EuroGOOS knowledge areas: European ocean observations, modelling and forecasting technology, coastal operational oceanography, and operational ecology.

Description: Deforestation decreases resistance of simulated Easter Island climate to drought Alexander Lemburg, Martin Claussen, and Felix Ament Clim. Past Discuss., doi:10.5194/cp-2016-68,2016 Manuscript under review for CP (discussion: open, 0 comments) The deforestation of Easter Island several hundred years ago might have influenced its local near-surface climate. With a series of numerical model experiments we investigate the impact of deforestation on precipitation and near-surface climate. We find that a deforested Easter Island appears to be significantly less resistant to drought than a forested island and thus, deforestation has probably exacerbated the effects of past climate drought spells on Easter Island's socio-ecological systems.

Description: Accelerated sea level rise and Florida Current transport Ocean Science Discussions, 12, 551-572, 2015 Author(s): J. Park and W. Sweet The Florida Current is the headwater of the Gulf Stream and is a component of the North Atlantic western boundary current from which a geostrophic balance between sea surface height and mass transport directly influence coastal sea levels along the Florida Straits. A linear regression of daily Florida Current transport estimates does not find a significant change in transport over the last decade, however, a nonlinear trend extracted from empirical mode decomposition suggests a 3 Sv decline in mean transport. This decline is consistent with observed tide gauge records in Florida Bay and the Straits, all exhibiting an acceleration of mean sea level rise over the decade. It is not known whether this recent change represents natural variability or the onset of the anticipated secular decline in Atlantic meridional overturning circulation, nonetheless, such changes have direct impacts on the sensitive ecological systems of the Everglades as well as the climate of western Europe and eastern North America.

Description: Sea level trends in Southeast Asian seas Climate of the Past, 11, 743-750, 2015 Author(s): M. W. Strassburg, B. D. Hamlington, R. R. Leben, P. Manurung, J. Lumban Gaol, B. Nababan, S. Vignudelli, and K.-Y. Kim Southeast Asian seas span the largest archipelago in the global ocean and provide a complex oceanic pathway connecting the Pacific and Indian oceans. The Southeast Asian sea regional sea level trends are some of the highest observed in the modern satellite altimeter record that now spans almost 2 decades. Initial comparisons of global sea level reconstructions find that 17-year sea level trends over the past 60 years exhibit good agreement with decadal variability associated with the Pacific Decadal Oscillation and related fluctuations of trade winds in the region. The Southeast Asian sea region exhibits sea level trends that vary dramatically over the studied time period. This historical variation suggests that the strong regional sea level trends observed during the modern satellite altimeter record will abate as trade winds fluctuate on decadal and longer timescales. Furthermore, after removing the contribution of the Pacific Decadal Oscillation (PDO) to sea level trends in the past 20 years, the rate of sea level rise is greatly reduced in the Southeast Asian sea region. As a result of the influence of the PDO, the Southeast Asian sea regional sea level trends during the 2010s and 2020s are likely to be less than the global mean sea level (GMSL) trend if the observed oscillations in wind forcing and sea level persist. Nevertheless, long-term sea level trends in the Southeast Asian seas will continue to be affected by GMSL rise occurring now and in the future.

Description: Non-linear regime shifts in Holocene Asian monsoon variability: potential impacts on cultural change and migratory patterns Climate of the Past, 11, 709-741, 2015 Author(s): J. F. Donges, R. V. Donner, N. Marwan, S. F. M. Breitenbach, K. Rehfeld, and J. Kurths The Asian monsoon system is an important tipping element in Earth's climate with a large impact on human societies in the past and present. In light of the potentially severe impacts of present and future anthropogenic climate change on Asian hydrology, it is vital to understand the forcing mechanisms of past climatic regime shifts in the Asian monsoon domain. Here we use novel recurrence network analysis techniques for detecting episodes with pronounced non-linear changes in Holocene Asian monsoon dynamics recorded in speleothems from caves distributed throughout the major branches of the Asian monsoon system. A newly developed multi-proxy methodology explicitly considers dating uncertainties with the COPRA (COnstructing Proxy Records from Age models) approach and allows for detection of continental-scale regime shifts in the complexity of monsoon dynamics. Several epochs are characterised by non-linear regime shifts in Asian monsoon variability, including the periods around 8.5–7.9, 5.7–5.0, 4.1–3.7, and 3.0–2.4 ka BP. The timing of these regime shifts is consistent with known episodes of Holocene rapid climate change (RCC) and high-latitude Bond events. Additionally, we observe a previously rarely reported non-linear regime shift around 7.3 ka BP, a timing that matches the typical 1.0–1.5 ky return intervals of Bond events. A detailed review of previously suggested links between Holocene climatic changes in the Asian monsoon domain and the archaeological record indicates that, in addition to previously considered longer-term changes in mean monsoon intensity and other climatic parameters, regime shifts in monsoon complexity might have played an important role as drivers of migration, pronounced cultural changes, and the collapse of ancient human societies.

Description: Simulation of tsunami generation, propagation and coastal inundation in the Eastern Mediterranean Ocean Science Discussions, 12, 673-699, 2015 Author(s): A. G. Samaras, T. V. Karambas, and R. Archetti In the present work, an advanced tsunami generation, propagation and coastal inundation 2-DH model (i.e. 2-D Horizontal model) based on the higher-order Boussinesq equations – developed by the authors – is applied to simulate representative earthquake-induced tsunami scenarios in the Eastern Mediterranean. Two areas of interest were selected after evaluating tsunamigenic zones and possible sources in the region: one at the Southwest of the island of Crete in Greece and one at the East of the island of Sicily in Italy. Model results are presented in the form of extreme water elevation maps, sequences of snapshots of water elevation during the propagation of the tsunamis, and inundation maps of the studied low-lying coastal areas. This work marks one of the first successful applications of a fully nonlinear model for the 2-DH simulation of tsunami-induced coastal inundation; acquired results are indicative of the model's capabilities, as well of how areas in the Eastern Mediterranean would be affected by eventual larger events.

Description: Northern Hemisphere control of deglacial vegetation changes in the Rufiji uplands (Tanzania) Climate of the Past, 11, 751-764, 2015 Author(s): I. Bouimetarhan, L. Dupont, H. Kuhlmann, J. Pätzold, M. Prange, E. Schefuß, and K. Zonneveld In tropical eastern Africa, vegetation distribution is largely controlled by regional hydrology, which has varied over the past 20 000 years. Therefore, accurate reconstructions of past vegetation and hydrological changes are crucial for a better understanding of climate variability in the tropical southeastern African region. We present high-resolution pollen records from a marine sediment core recovered offshore of the Rufiji River delta. Our data document significant shifts in pollen assemblages during the last deglaciation, identifying, through changes in both upland and lowland vegetation, specific responses of plant communities to atmospheric (precipitation) and coastal (coastal dynamics and sea-level changes) alterations. Specifically, arid conditions reflected by a maximum pollen representation of dry and open vegetation occurred during the Northern Hemisphere cold Heinrich event 1 (H1), suggesting that the expansion of drier upland vegetation was synchronous with cold Northern Hemisphere conditions. This arid period is followed by an interval in which forest and humid woodlands expanded, indicating a hydrologic shift towards more humid conditions. Droughts during H1 and the shift to humid conditions around 14.8 kyr BP in the uplands are consistent with latitudinal shifts of the intertropical convergence zone (ITCZ) driven by high-latitude Northern Hemisphere climatic fluctuations. Additionally, our results show that the lowland vegetation, consisting of well-developed salt marshes and mangroves in a successional pattern typical for vegetation occurring in intertidal habitats, has responded mainly to local coastal dynamics related to marine inundation frequencies and soil salinity in the Rufiji Delta as well as to the local moisture availability. Lowland vegetation shows a substantial expansion of mangrove trees after ~ 14.8 kyr BP, suggesting an increased moisture availability and river runoff in the coastal area. The results of this study highlight the decoupled climatic and environmental processes to which the vegetation in the uplands and the Rufiji Delta has responded during the last deglaciation.

Description: A 2000-year annual record of snow accumulation rates for Law Dome, East Antarctica Climate of the Past, 11, 697-707, 2015 Author(s): J. Roberts, C. Plummer, T. Vance, T. van Ommen, A. Moy, S. Poynter, A. Treverrow, M. Curran, and S. George Accurate high-resolution records of snow accumulation rates in Antarctica are crucial for estimating ice sheet mass balance and subsequent sea level change. Snowfall rates at Law Dome, East Antarctica, have been linked with regional atmospheric circulation to the mid-latitudes as well as regional Antarctic snowfall. Here, we extend the length of the Law Dome accumulation record from 750 years to 2035 years, using recent annual layer dating that extends to 22 BCE. Accumulation rates were calculated as the ratio of measured to modelled layer thicknesses, multiplied by the long-term mean accumulation rate. The modelled layer thicknesses were based on a power-law vertical strain rate profile fitted to observed annual layer thickness. The periods 380–442, 727–783 and 1970–2009 CE have above-average snow accumulation rates, while 663–704, 933–975 and 1429–1468 CE were below average, and decadal-scale snow accumulation anomalies were found to be relatively common (74 events in the 2035-year record). The calculated snow accumulation rates show good correlation with atmospheric reanalysis estimates, and significant spatial correlation over a wide expanse of East Antarctica, demonstrating that the Law Dome record captures larger-scale variability across a large region of East Antarctica well beyond the immediate vicinity of the Law Dome summit. Spectral analysis reveals periodicities in the snow accumulation record which may be related to El Niño–Southern Oscillation (ENSO) and Interdecadal Pacific Oscillation (IPO) frequencies.

Description: The RADMED monitoring program: towards an ecosystem approach Ocean Science Discussions, 12, 645-671, 2015 Author(s): J. L. López-Jurado, R. Balbín, B. Amengual, A. Aparicio-González, M. L. Fernández de Puelles, M. C. García-Martínez, M. Gazá, J. Jansá, A. Morillas-Kieffer, F. Moyá, R. Santiago, M. Serra, M. Vargas-Yáñez, and L. Vicente In the Western Mediterranean, the IEO-RADMED monitoring program is already conducting many of the evaluations required under the Marine Strategy Framework Directive (MFSD) along the Spanish Mediterranean coast. The different aspects of the ecosystem that are regularly sampled under this monitoring program are the physical environment and the chemical and biological variables of the water column, together with the planktonic communities, biomass and structure. Moreover, determinations of some anthropogenic stressors on the marine environment, as contaminants and microplastics, are under develop. Data are managed and stored at the IEO Data Center that works under the SeaDataNet infrastructure and are also stored under the IBAMar database. In combination with remote sensing data they are used to address open questions on the ecosystem in the Western Mediterranean sea.

Description: Carbon-based phytoplankton size classes retrieved via ocean color estimates of the particle size distribution Ocean Science Discussions, 12, 573-644, 2015 Author(s): T. S. Kostadinov, S. Milutinović, I. Marinov, and A. Cabré Owing to their important roles in biogeochemical cycles, phytoplankton functional types (PFTs) have been the aim of an increasing number of ocean color algorithms. Yet, none of the existing methods are based on phytoplankton carbon (C) biomass, which is a fundamental biogeochemical and ecological variable and the "unit of accounting" in Earth System models. We present a novel bio-optical algorithm to retrieve size-partitioned phytoplankton carbon from ocean color satellite data. The algorithm is based on existing algorithms to estimate particle volume from a power-law particle size distribution (PSD). Volume is converted to carbon concentrations using a compilation of allometric relationships. We quantify absolute and fractional biomass in three PFTs based on size – picophytoplankton (0.5–2 μm in diameter), nanophytoplankton (2–20 μm) and microphytoplankton (20–50 μm). The mean spatial distributions of total phytoplankton C biomass and individual PFTs, derived from global SeaWiFS monthly ocean color data, are consistent with current understanding of oceanic ecosystems, i.e. oligotrophic regions are characterized by low biomass and dominance of picoplankton, whereas eutrophic regions have large biomass to which nanoplankton and microplankton contribute relatively larger fractions. Global spatially integrated phytoplankton carbon biomass standing stock estimates using our PSD-based approach yield on average ~0.2–0.3 Gt of C, consistent with analogous estimates from two other ocean color algorithms, and several state-of-the-art Earth System models. However, the range of phytoplankton C biomass spatial variability globally is larger than estimated by any other models considered here, because the PSD-based algorithm is not a priori empirically constrained and introduces improvement over the assumptions of the other approaches. Satisfactory in situ closure observed between PSD and POC measurements lends support to the theoretical basis of the PSD-based algorithm. Uncertainty budget analyses indicate that absolute carbon concentration uncertainties are driven by the PSD parameter N o which determines particle number concentration to first order, while uncertainties in PFTs' fractional contributions to total C biomass are mostly due to the allometric coefficients.

Description: Sea level budget over 2005–2013: missing contributions and data errors Ocean Science Discussions, 12, 701-734, 2015 Author(s): H. B. Dieng, A. Cazenave, K. von Schuckmann, M. Ablain, and B. Meyssignac Based on the sea level budget closure approach, this study investigates the residuals between observed global mean sea level (GMSL) and the sum of components (steric sea level and ocean mass) for the period January 2005 to December 2013. The objective is to identify the impact of errors in one or several components of the sea level budget on the residual time series. This is a key issue if we want to constrain missing contributions such as the contribution to sea level rise from the deep ocean (〉 2000m). For that purpose, we use several data sets as processed by different groups: six altimetry products for the GMSL, four Argo products plus the ORAS4 ocean reanalysis for the steric sea level and three GRACE-based ocean mass products. We find that over the study time span, the observed trend differences in the residuals of the sea level budget can be as large as ~0.55mm yr −1 . These trend differences essentially result from the processing of the altimetry data (e.g., choice the geophysical corrections and method of averaging the along-track altimetry data). At short time scale (from sub-seasonal to multi-annual), residual anomalies are significantly correlated with ocean mass and steric sea level anomalies (depending on the time span), indicating that the residual anomalies are related to errors in both GRACE-based ocean mass and Argo-based steric data. Efforts are needed to reduce these various sources of errors before using the sea level budget approach to estimate missing contributions such as the deep ocean heat content.

Description: The WAIS Divide deep ice core WD2014 chronology – Part 1: Methane synchronization (68–31 ka BP) and the gas age–ice age difference Climate of the Past, 11, 153-173, 2015 Author(s): C. Buizert, K. M. Cuffey, J. P. Severinghaus, D. Baggenstos, T. J. Fudge, E. J. Steig, B. R. Markle, M. Winstrup, R. H. Rhodes, E. J. Brook, T. A. Sowers, G. D. Clow, H. Cheng, R. L. Edwards, M. Sigl, J. R. McConnell, and K. C. Taylor The West Antarctic Ice Sheet Divide (WAIS Divide, WD) ice core is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ∼68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8–31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WD gas age–ice age difference (Δage) using a combination of firn densification modeling, ice-flow modeling, and a data set of δ 15 N-N 2 , a proxy for past firn column thickness. The largest Δage at WD occurs during the Last Glacial Maximum, and is 525 ± 120 years. Internally consistent solutions can be found only when assuming little to no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WD chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard–Oeschger (DO) events into agreement with the U/Th absolutely dated Hulu Cave speleothem record. The small Δage at WD provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the "bipolar seesaw".

Description: Effects of surface current/wind interaction in an eddy-rich general ocean circulation simulation of the Baltic Sea H. Dietze and U. Löptien Ocean Sci. Discuss., doi:10.5194/os-2016-12,2016 Manuscript under review for OS (discussion: open, 0 comments) Winds blowing over the ocean drive ocean currents. The oceanic response to winds is, in turn, influenced by ocean currents. Theoretical considerations suggest that the latter effect is especially pronounced in the Baltic Sea where the spatial scale of current variability is much smaller than in the open ocean. The study presented here puts theses theoretical considerations in a high-resolution ocean circulation model of the Baltic Sea to the test.

Description: Mode transitions in Northern Hemisphere Glaciation: Co-evolution of millennial and orbital variability in Quaternary climate David A. Hodell and James E.T. Channell Clim. Past Discuss., doi:10.5194/cp-2016-30,2016 Manuscript under review for CP (discussion: open, 0 comments) For the past 2.7 million years the Earth’s climate has switched more than 50 times between a cold glacial and warm interglacial state. We found the trend towards larger ice sheets over the past 2.7 million years was accompanied by changes in the style, frequency and intensity of shorter-term (millennial) variability. We suggest the interaction between millennial climate change and longer-term variations in the Earth's orbit may be important for explaining the patterns of Quaternary climate.

Description: The WAIS Divide deep ice core WD2014 chronology – Part 2: Annual-layer counting (0–31 ka BP) Michael Sigl, Tyler J. Fudge, Mai Winstrup, Jihong Cole-Dai, David Ferris, Joseph R. McConnell, Ken C. Taylor, Kees C. Welten, Thomas E. Woodruff, Florian Adolphi, Marion Bisiaux, Edward J. Brook, Christo Buizert, Marc W. Caffee, Nelia W. Dunbar, Ross Edwards, Lei Geng, Nels Iverson, Bess Koffman, Lawrence Layman, Olivia J. Maselli, Kenneth McGwire, Raimund Muscheler, Kunihiko Nishiizumi, Daniel R. Pasteris, Rachael H. Rhodes, and Todd A. Sowers Clim. Past, 12, 769-786, doi:10.5194/cp-12-769-2016, 2016 Here we present a chronology (WD2014) for the upper part (0–2850 m; 31.2 ka BP) of the West Antarctic Ice Sheet (WAIS) Divide ice core, which is based on layer counting of distinctive annual cycles preserved in the elemental, chemical and electrical conductivity records. We validated the chronology by comparing it to independent high-accuracy, absolutely dated chronologies. Given its demonstrated high accuracy, WD2014 can become a reference chronology for the Southern Hemisphere.

Description: Terrigenous material supply to the Peruvian central continental shelf (Pisco, 14° S) during the last 1000 years: paleoclimatic implications Francisco Javier Briceño-Zuluaga, Abdelfettah Sifeddine, Sandrine Caquineau, Jorge Cardich, Renato Salvatteci, Dimitri Gutierrez, Luc Ortlieb, Federico Velazco, Hugues Boucher, and Carine Machado Clim. Past, 12, 787-798, doi:10.5194/cp-12-787-2016, 2016 Comparison between records reveals a coherent match between the meridional displacement of the ITCZ-SPSH system and the regional fluvial and aeolian terrigenous input variability. The aeolian input intensity and the anoxic conditions recorded by marine sediments showed a close link that suggests a common mechanism associated with SPSH displacement. Changes in sediment discharge to the continental shelf are linked to the southward displacement of the ITCZ-SPSH and Walker circulation.

Description: Solar modulation of flood frequency in central Europe during spring and summer on interannual to multi-centennial timescales Markus Czymzik, Raimund Muscheler, and Achim Brauer Clim. Past, 12, 799-805, doi:10.5194/cp-12-799-2016, 2016 Integrating discharge data of the River Ammer back to 1926 and a 5500-year flood layer record from an annually laminated sediment core of the downstream Ammersee allowed investigating changes in the frequency of major floods in Central Europe on interannual to multi-centennial timescales. Significant correlations between flood frequency variations in both archives and changes in the activity of the Sun suggest a solar influence on the frequency of these hydrometeorological extremes.

Description: Constraints on ocean circulation at the Paleocene–Eocene Thermal Maximum from neodymium isotopes April N. Abbott, Brian A. Haley, Aradhna K. Tripati, and Martin Frank Clim. Past, 12, 837-847, doi:10.5194/cp-12-837-2016, 2016 The Paleocene-Eocene Thermal Maximum (PETM) was a brief period when the Earth was in an extreme greenhouse state. We use neodymium isotopes to suggest that during this time deep-ocean circulation was distinct in each basin (North and South Atlanic, Southern, Pacific) with little exchange between. Moreover, the Pacific data show the most variability, suggesting this was a critical region possibly involved in both PETM triggering and remediation.