ALBERT

Description: Thriving benthic communities were observed in the oxygen minimum zones along the southwestern African margin. On the Namibian margin, fossil cold-water coral mounds were overgrown by sponges and bryozoans, while the Angolan margin was characterized by cold-water coral mounds covered by a living coral reef. To explore why benthic communities differ in both areas, present-day environmental conditions were assessed, using conductivity–temperature–depth (CTD) transects and bottom landers to investigate spatial and temporal variations of environmental properties. Near-bottom measurements recorded low dissolved oxygen concentrations on the Namibian margin of 0–0.15 mL L−1 (≜0 %–9 % saturation) and on the Angolan margin of 0.5–1.5 mL L−1 (≜7 %–18 % saturation), which were associated with relatively high temperatures (11.8–13.2 ∘C and 6.4–12.6 ∘C, respectively). Semidiurnal barotropic tides were found to interact with the margin topography producing internal waves. These tidal movements deliver water with more suitable characteristics to the benthic communities from below and above the zone of low oxygen. Concurrently, the delivery of a high quantity and quality of organic matter was observed, being an important food source for the benthic fauna. On the Namibian margin, organic matter originated directly from the surface productive zone, whereas on the Angolan margin the geochemical signature of organic matter suggested an additional mechanism of food supply. A nepheloid layer observed above the cold-water corals may constitute a reservoir of organic matter, facilitating a constant supply of food particles by tidal mixing. Our data suggest that the benthic fauna on the Namibian margin, as well as the cold-water coral communities on the Angolan margin, may compensate for unfavorable conditions of low oxygen levels and high temperatures with enhanced availability of food, while anoxic conditions on the Namibian margin are at present a limiting factor for cold-water coral growth. This study provides an example of how benthic ecosystems cope with such extreme environmental conditions since it is expected that oxygen minimum zones will expand in the future due to anthropogenic activities.

Description: Living benthic foraminifera of Flensburg Fjord were surveyed in June 2006. The muddy and organic-rich sediments of the inner fjord were dominated by Elphidium incertum. E. incertum and E. excavatum were frequent in muds and sandy muds of the fjord loop around Holnis Peninsula and in the outer part. Gelting Bay yielded a different biofacies, indicating a brackish and sandy habitat, poor in food supply and with microfauna dominated by Ammonia beccarii and E. albiumbilicatum. The central fjord and nearshore zones of the loop were characterized by sandy muds, relatively poor in food and occupied by A. beccarii, E. incertum and E. excavatum subspecies. High abundances of E. excavatum were encountered in the innermost fjord, with fine-grained and organic-rich muddy sediments.A comparison with previous studies revealed the profound changes in species composition in the outer Flensburg Fjord since the 1970s. A decline in numbers of Ammotium cassis and flourishing of Ammonia beccarii in Gelting Bay were recognized. These changes are most likely associated with decreased intensity and frequency of salt-water inflows into the Baltic Sea since the 1960s. It is inferred that the decline of A. cassis is similar to that of Eggerelloides scaber, which currently is found only in depressions of Kiel Bight with higher salinity.

Description: Fossil cold-water coral mounds overgrown by sponges and bryozoans were observed in anoxic conditions on the Namibian margin, while mounds colonized by thriving cold-water coral reefs were found in hypoxic conditions on the Angolan margin. These low oxygen conditions do not meet known environmental ranges favoring cold-water corals and hence are expected to provide unsuitable habitats for cold-water coral growth and therefore reef formation. To explain why the living fauna can nevertheless thrive in both areas, present day environmental conditions at the southwestern African margin were assessed. Downslope CTD transects and the deployment of bottom landers were used to investigate spatial and temporal variations of environmental properties. Temporal measurements in the mound areas recorded oscillating low dissolved oxygen concentrations of 0–0.17 ml l−1 (≙ 0–9 % saturation) on the Namibian and 0.5–1.5 ml l−1 (≙ 7–18 % saturation) on the Angolan margin, which were associated with relatively high temperatures (11.8 13.2 °C and 6.4–12.6 °C respectively). Semi-diurnal barotrophic tides were found to interact with the margin topography producing internal waves with excursions of up to 70 and 130 m for the Namibian and Angolan margins, respectively. These tidal movements temporarily deliver water with more suitable characteristics to the coral mounds from below and above the hypoxic zone. Concurrently, the delivery of high quantity and quality of suspended particulate organic matter was observed, which serves as a food source for cold-water corals. On the Namibian slope organic matter indicates a completely marine source and originates directly from the surface productive zone, whereas on the Angolan margin the geochemical signature of organic material suggest an additional mechanisms of food supply. A nepheloid layer observed above the cold-water coral mound area on the Angolan margin may constitutes a reservoir of fresh organic matter, facilitating a constant supply of food particles by tidal mixing. This suggests that the cold-water coral communities as well as the associated fauna may compensate unfavorable conditions induced by low oxygen levels and high temperatures with an enhanced availability of food. With the expected expansion of oxygen minimum zones in the future due to anthropogenic activities, this study provides an example on how ecosystems could cope with such extreme environmental conditions.

Description: The rising temperature of the world’s oceans is affecting coral reef ecosystems by increasing the frequency and severity of bleaching and mortality events. The susceptibility of corals to temperature stress varies on local and regional scales. Insights into potential controlling parameters are hampered by a lack of long term in situ data in most coral reef environments and sea surface temperature (SST) products often do not resolve reef-scale variations. Here we use 42 years (1970–2012) of coral Sr/Ca data to reconstruct seasonal- to decadal-scale SST variations in two adjacent but distinct reef environments at Little Cayman, Cayman Islands. Our results indicate that two massive Diploria strigosa corals growing in the lagoon and in the fore reef responded differently to past warming events. Coral Sr/Ca data from the shallow lagoon successfully record high summer temperatures confirmed by in situ observations (〉338C). Surprisingly, coral Sr/Ca from the deeper fore reef is strongly affected by thermal stress events, although seasonal temperature extremes and mean SSTs at this site are reduced compared to the lagoon. The shallow lagoon coral showed decadal variations in Sr/Ca, supposedly related to the modulation of lagoonal temperature through varying tidal water exchange, influenced by the 18.6 year lunar nodal cycle. Our results show that reef-scale SST variability can be much larger than suggested by satellite SST measurements. Thus, using coral SST proxy records from different reef zones combined with in situ observations will improve conservation programs that are developed to monitor and predict potential thermal stress on coral reefs.

Description: Here we present the first record of Sr/Ca variability in a massive Porites lutea coral from the Lakshadweep Archipelago, Arabian Sea. The annual mean sea surface temperature (SST) in this region and the surrounding areas has increased steadily in the recent past. During some major El Nino events, SSTs are even higher, imposing additional thermal-stress on corals, episodically leading to coral bleaching. We infer from the coral-Sr/Ca record (1981-2008) that during some of these events high and persistent SSTs lead to a dampening of the temperature signal in coral-Sr/Ca, impairing the coral's ability to record full scale warming. Thus, coral-Sr/Ca may provide a history of past El Nino Southern-Oscillation (ENSO) induced thermal-stress episodes, which are a recurrent feature also seen in cross-spectral analysis between coral-Sr/Ca and the Nino3.4 index. Despite the impact of episodical thermal-stress during major El Nino events, our coral proxy faithfully records the seasonal monsoon-induced summer cooling on the order of approximate to 2.3 degrees C. Calibration of coral-Sr/Ca with instrumental grid-SST data shows significant correlation to regional SST and monsoon variability. Hence, massive Porites corals of this region are highly valuable archives for reconstructing long-term changes in SST, strongly influenced by monsoon variability on seasonal scales. More importantly, our data show that this site with increasing SST is an ideal location for testing the future effects of the projected anthropogenic SST increase on coral reefs that are already under thermal-stress worldwide.

Description: EGU2010-2934 The exploration of the arctic seas require an integrated approach applying different infrastructures. In Fall 2009 German and Russian scientists performed a geo marine cruise off Kamchatka and in the western Bering Sea within the frame of the KALMAR-Project. Two main research subjects formed the scientific backbone of the cruise: The first objective focuses on the geodynamic and volcanological magmatic development of the Kuril-Kamchatka island arc system and the Kamchatka Aleutean Islands Triple-Junction. Very little is known about the composition of the mantle and the oceanic crust as well as of the seamounts including their ages. The best studied site is the Volcanologist’s Massif located between the Bering- and the Alpha Fracture Zone (Tsvetkov 1990, Volynets et al. 1992, Yogodzinsky et al. 1994), which structurally belongs to the Komandorsky Basin. The oldest rocks of the Volcanologist´s Massif show very similar trace element and isotope signatures like those rocks cropping out in the volcanoes on Kamchatka in the prolongation of the Alpha Fracture Zone (Portnyagin et al. 2005a), indicating similar conditions of magma formation. The top of the Volcanologist´s Massif is characterized by the young (〈 0.5 Ma) and hydrothermally active Piip volcano, which consists of special magnesium rich andesites ("Piip type"). Another hot site was the Meiji-Seamount which is the northernmost Seamount of the hotspot spur of the Hawaii-Emperor-Seamount chain, having an age of probably 〉 85 Ma. The only existing basement rocks from this seamount were gained during DSDP Leg 19. These are basalts with MORB like trace element and isotope signatures (Keller et al. 2000, Regelous et al. 2003). These data indicate that the Hawaii-Hotspot was at a MOR in Cretaceous time and that large volumes of depleted mantle material played a´role during the magma formation. The second objective focuses on paleo-oceanographic investigations concentrating on the sediments along the eastern continental slope of Kamchatka, in the Komandorsky Basin, and on the Shirshov Ridge in order to explore paleoclimate archives to better understand the subpolar water mass transfer and the oceanographic and climatic development in the subarctic NW-Pacific. Comparisons of Late Pleistocene and Holocene temperature changes within the near surface water masses between the NW-Pacific and the N-Atlantic resulted in a new hypothesis, the "Atlantic-Pacific seesaw" (Kiefer et al. 2001, Kim et al. 2004, Kiefer and Kienast, 2005). This Atlantic-Pacific pattern of opposite temperature variations dominates the last 60ka on millennial timescales. Modelling results of Saenko et al. (2004) support the hypothesis of the "Atlantic-Pacific seesaw" and they postulate a mechanistic connection between the two regions driven by salinity variations, which couples both regions through the thermohaline circulation. A different model relates the Holocene Atlantic-Pacific dipole to the atmospheric tele-connection between the Arctic Oscillation/N-Atlantic Oscillation and the Pacific N-American Oscillation (Kim et al. 2004). http://kalmar.ifm-geomar.de

Description: Precisely quantifying the current climate-related sea level change requires accurate knowledge of long-term geological processes known as Glacial Isostatic Adjustments (GIA). Although the major postglacial melting phase is likely to have ended ∼6–4 ka BP (before present), GIA is still significantly affecting the present-day vertical position of the mean sea surface and the sea bottom. Here we present empirical rsl (relative sea level) data based on U/Th dated fossil corals from reef platforms of the Society Islands, French Polynesia, together with the corresponding GIA-modeling. Fossil coral data constrain the timing and amplitude of rsl variations after the Holocene sea level maximum (HSLM). Upon correction for isostatic island subsidence, we find that local rsl was at least ∼1.5 ± 0.4 m higher than present at ∼5.4 ka. Later, minor amplitude variations occurred until ∼2 ka, when the rsl started dropping to its present position with a rate of ∼0.4 mm/yr. The data match with predicted rsl curves based on global ice-sheet chronologies confirming the role of GIA-induced ocean siphoning effect throughout the mid to late Holocene. A long lasting Late Holocene highstand superimposed with second-order amplitudinal fluctuations as seen from our data suggest that the theoretical predicted timing of rsl change can still be refined pending future calibration.

Description: The Indonesian Throughflow (ITF), which represents the global ocean circulation connecting the Pacific Warm Pool to the Indian Ocean, strongly influences the Indo-Pacific climate. ITF monitoring since the late 1990s using mooring buoys have provided insights on seasonal and interannual time scales. However, the absence of longer records limits our perspective on its evolution over the past century. Here, we present sea surface temperature (SST) and salinity (SSS) proxy records from Timor Island located at the ITF exit passage via paired coral δ18O and Sr/Ca measurements spanning the period 1914–2004. These high-resolution proxy based climate data of the last century highlights improvements and cautions when interpreting paleoclimate records of the Indonesian region. If the seasonality of SST and SSS is not perfectly in phase, the application of coral Sr/Ca thermometry improves SST reconstructions compared to estimates based on coral δ18O only. Our records also underline the importance of ocean advection besides rainfall on local SSS in the region. Although the El Niño/Southern Oscillation (ENSO) causes larger anomalies relative to the Indian Ocean Dipole (IOD), Timor coral-based SST and SSS records robustly correlate with IOD on interannual time scales, whereas ENSO only modifies Timor SST. Similarly, Timor SST and SSS are strongly linked to Indian Ocean decadal-scale variations that appear to lead Timor oceanographic conditions by about 1.6–2 years. Our study sheds new light on the complex signatures of Indo-Pacific climate modes on SST and SSS dynamics of the ITF.

Description: Sea surface salinity (SSS) is an important variable in the global ocean circulation. However, decadal to interdecadal changes in SSS are not well understood due to the lack of instrumental data. Here we reconstruct SSS from a paired, bimonthly resolved coral δ18O and Sr/Ca record from La Reunion Island that extends from 1913 to 1995. Coral Sr/Ca correlates with regional sea surface temperature (SST) back to 1966, when instrumental coverage is good, while coral δ18O does not. The slope of the monthly (annual mean) coral Sr/Ca-SST regression is −0.040 mmol/mol per 1 °C (−0.068 mmol/mol per 1 °C) consistent with published estimates of the Sr/Ca-SST relationship. Coral Sr/Ca suggest a warming of 0.39 °C since 1913. δ18O seawater is calculated by subtracting the temperature component from measured coral δ18O, using coral Sr/Ca as well as historical SST products. The derived δ18O seawater reconstructions are correlated (r 〉 0.6), and all show a significant shift in the midtwentieth century (−0.17‰ to −0.19‰), indicating a freshening of SSS by 0.7 psu. However, the timing of this shift depends on the temperature component and varies from 1947 (δ18O seawater calculated with historical SST) to the late 1950s (δ18O seawater calculated with coral Sr/Ca). Coral Sr/Ca shows warm temperature anomalies in the mid-1950s, while historical SST products show warm anomalies from 1940 to 1945 followed by cooling in the 1950s, a pattern typical for the World War II bias. This suggests that historical SST may bias reconstructions of δ18O seawater and SSS from corals.