ALBERT

Description: Trace metals (Cd, Cu, Pb and Zn) were analysed in different well-defined mixed copepod and euphausiid samples as well as in individually analysed decapods collected during a cruise on board “RV Walther Herwig III” to the Iberian Deep Sea Plain in March and April, 2002. We found a substantial interspecific heterogeneity with partially high mean Cd levels in the decapods: 1.9 mg kg-1 dry weight in samples of the genus Sergia; 6.1 mg kg-1 in Acanthephyra pelagica (Risso, 1816) and Acanthephyra acanthithelsonis Bate, 1888; 10.7 mg kg-1 in Bentheogennema intermedia (Bate, 1888); 14.9 mg kg-1 in Benthesicymus iridescens (Bate 1881) and 16.3 mg kg-1 in Systellaspis debilis (A. Milne Edwards, 1881). The agreement of these high Cd concentrations with those reported for polar crustaceans, and Cu concentrations (17–56 mg kg-1) that indicate that the total metabolic requirements have probably not been met, support the hypothesis that the frequently reported Cd-anomaly in polar crustaceans might be extended to other relatively deep ocean waters like the Iberian Deep Sea Plain and that this might be related to a corresponding Cu deficiency. Zn concentrations in decapods from this study (52–80 mg kg-1) are within the worldwide range, which indicates that decapods are able to regulate their Zn body concentrations. Our preliminary data on mixed zooplankton samples suggest that Pb concentrations far below 1 mg Pb kg-1 might serve as a regional background value for comparison in biomonitoring studies. Results for Cd, Cu and Zn are largely within the reported range, especially for data from the Central and Southern North Sea.

Description: The coastal ocean is a crucial link between land, the open ocean and the atmosphere. The shallowness of the water column permits close interactions between the sedimentary, aquatic and atmospheric compartments, which otherwise are decoupled at long time scales (≅ 1000 yr) in the open oceans. Despite the prominent role of the coastal oceans in absorbing atmospheric CO2 and transferring it into the deep oceans via the continental shelf pump, the underlying mechanisms remain only partly understood. Evaluating observations from the North Sea, a NW European shelf sea, we provide evidence that anaerobic degradation of organic matter, fuelled from land and ocean, generates total alkalinity (AT) and increases the CO2 buffer capacity of seawater. At both the basin wide and annual scales anaerobic AT generation in the North Sea's tidal mud flat area irreversibly facilitates 7–10%, or taking into consideration benthic denitrification in the North Sea, 20–25% of the North Sea's overall CO2 uptake. At the global scale, anaerobic AT generation could be accountable for as much as 60% of the uptake of CO2 in shelf and marginal seas, making this process, the anaerobic pump, a key player in the biological carbon pump. Under future high CO2 conditions oceanic CO2 storage via the anaerobic pump may even gain further relevance because of stimulated ocean productivity.

Description: The mechanisms driving the air–sea exchange of carbon dioxide (CO2CO2) in the North Sea are investigated using the three-dimensional coupled physical–biogeochemical model ECOHAM (ECOlogical-model, HAMburg). We validate our simulations using field data for the years 2001–2002 and identify the controls of the air–sea CO2CO2 flux for two locations representative for the North Sea's biogeochemical provinces. In the seasonally stratified northern region, net CO2CO2 uptake is high (View the MathML source2.06molm-2a-1) due to high net community production (NCP) in the surface water. Overflow production releasing semi-labile dissolved organic carbon needs to be considered for a realistic simulation of the low dissolved inorganic carbon (DIC) concentrations observed during summer. This biologically driven carbon drawdown outcompetes the temperature-driven rise in CO2CO2 partial pressure (pCO2pCO2) during the productive season. In contrast, the permanently mixed southern region is a weak net CO2CO2 source (View the MathML source0.78molm-2a-1). NCP is generally low except for the spring bloom because remineralization parallels primary production. Here, the pCO2pCO2 appears to be controlled by temperature.

Description: Observational studies report a rapid decline of ocean CO2 uptake in the temperate North Atlantic during the last decade. We analyze these findings using ocean physical‐biological numerical simulations forced with interannually varying atmospheric conditions for the period 1979–2004. In the simulations, surface ocean water mass properties and CO2 system variables exhibit substantial multiannual variability on sub‐basin scales in response to wind‐driven reorganization in ocean circulation and surface warming/cooling. The simulated temporal evolution of the ocean CO2 system is broadly consistent with reported observational trends and is influenced substantially by the phase of the North Atlantic Oscillation (NAO). Many of the observational estimates cover a period after 1995 of mostly negative or weakly positive NAO conditions, which are characterized in the simulations by reduced North Atlantic Current transport of subtropical waters into the eastern basin and by a decline in CO2 uptake. We suggest therefore that air‐sea CO2 uptake may rebound in the eastern temperate North Atlantic during future periods of more positive NAO, similar to the patterns found in our model for the sustained positive NAO period in the early 1990s. Thus, our analysis indicates that the recent rapid shifts in CO2 flux reflect decadal perturbations superimposed on more gradual secular trends. The simulations highlight the need for long‐term ocean carbon observations and modeling to fully resolve multiannual variability, which can obscure detection of the long‐term changes associated with anthropogenic CO2 uptake and climate change.

Description: Diatoms account for up to 40% of marine primary production and require silicic acid to grow and build their opal shell. On the physiological and ecological level, diatoms are thought to be resistant to, or even benefit from, ocean acidification. Yet, global-scale responses and implications for biogeochemical cycles in the future ocean remain largely unknown. Here we conducted five in situ mesocosm experiments with natural plankton communities in different biomes and find that ocean acidification increases the elemental ratio of silicon (Si) to nitrogen (N) of sinking biogenic matter by 17 ± 6 per cent under pCO2 conditions projected for the year 2100. This shift in Si:N seems to be caused by slower chemical dissolution of silica at decreasing seawater pH. We test this finding with global sediment trap data, which confirm a widespread influence of pH on Si:N in the oceanic water column. Earth system model simulations show that a future pH-driven decrease in silica dissolution of sinking material reduces the availability of silicic acid in the surface ocean, triggering a global decline of diatoms by 13–26 per cent due to ocean acidification by the year 2200. This outcome contrasts sharply with the conclusions of previous experimental studies, thereby illustrating how our current understanding of biological impacts of ocean change can be considerably altered at the global scale through unexpected feedback mechanisms in the Earth system.