ALBERT

Description: Chloropigments and their derivative pheopigments preserved in sediments can directly be linked to photosynthesis. Their carbon and nitrogen stable isotopic compositions have been shown to be a good recorder of recent and past surface ocean environmental conditions tracing the carbon and nitrogen sources and dominant assimilation processes of the phytoplanktonic community. In this study we report results from combined compound-specific radiocarbon and stable carbon and nitrogen isotope analysis to examine the time-scales of synthesis and fate of chlorophyll-a and its degradation products pheophytin-a, pyropheophytin-a, and 132,173-cyclopheophorbide-a-enol until burial in Black Sea core-top sediments. The pigments are mainly of marine phytoplanktonic origin as implied by their stable isotopic compositions. Pigment ?15N values indicate nitrate as the major uptake substrate but 15N-depletion towards the open marine setting indicates either contribution from N2-fixation or direct uptake of ammonium from deeper waters. Radiocarbon concentrations translate into minimum and maximum pigment ages of approximately 40 to 1200 years. This implies that protective mechanisms against decomposition such as association with minerals, storage in deltaic anoxic environments, or eutrophication-induced hypoxia and light limitation are much more efficient than previously thought. Moreover, seasonal variations of nutrient source, growth period, and habitat and their associated isotopic variability are likely at least as strong as long-term trends. Combined triple isotope analysis of sedimentary chlorophyll and its primary derivatives is a powerful tool to delineate biogeochemical and diagenetic processes in the surface water and sediments, and to assess their precise time-scales.

Description: The early Pliocene warm phase was characterized by high sea surface temperatures and a deep thermocline in the eastern equatorial Pacific. A new hypothesis suggests that the progressive closure of the Panamanian seaway contributed substantially to the termination of this zonally symmetric state in the equatorial Pacific. According to this hypothesis, intensification of the Atlantic meridional overturning circulation (AMOC) - induced by the closure of the gateway - was the principal cause of equatorial Pacific thermocline shoaling during the Pliocene. In this study, twelve Panama seaway sensitivity experiments from eight ocean/climate models of different complexity are analyzed to examine the effect of an open gateway on AMOC strength and thermocline depth. All models show an eastward Panamanian net throughflow, leading to a reduction in AMOC strength compared to the corresponding closed-Panama case. In those models that do not include a dynamic atmosphere, deepening of the equatorial Pacific thermocline appears to scale almost linearly with the throughflow-induced reduction in AMOC strength. Models with dynamic atmosphere do not follow this simple relation. There are indications that in four out of five models equatorial wind-stress anomalies amplify the tropical Pacific thermocline deepening. In summary, the models provide strong support for the hypothesized relationship between Panama closure and equatorial Pacific thermocline shoaling.

Description: Radiocarbon (14C) dating calibration for the last glacial period largely relies on cross-dated marine 14C records. However, marine reservoirs are isotopically depleted with respect to the atmosphere, and therefore have to be corrected by the Marine Radiocarbon Ages of surface waters (MRAs), whose temporal variabilities are largely unknown. Here, we present simulations of the spatial and temporal variability in MRAs using a three-dimensional ocean circulation model covering the past 50,000 years. Our simulations are compared to reconstructions of past surface ocean D14C. Running the model with different climatic boundary conditions, we find that low- to mid-latitude MRAs have varied between 400 and 1200 14C years, with values of about 780 14C years at the Last Glacial Maximum. Reservoir ages exceeding 2000 14C years are simulated in the polar oceans. Our simulation results can be used as first order approximation of the MRA variability in future radiocarbon calibration efforts.

Description: Beyond ~13.9 cal kBP, the IntCal19 radiocarbon calibration curve is based upon combining data across a range of different archives including corals and planktic foraminifera. In order to reliably incorporate such marine data into an atmospheric curve, we need to resolve these records into their constituent atmospheric signal and marine reservoir age. This dataset includes results of marine reservoir age simulations enabling this resolution, applying the LSG ocean general circulation model forced with various climatic background conditions and with atmospheric radiocarbon changes according to the Hulu Cave speleothem record. Simulation period is 54,000-10,700 cal BP, depth range is 0-50 m. Land values are flagged with -100. This dataset is an update of PANGAEA datasets doi:10.1594/PANGAEA.876733 and doi:10.1594/PANGAEA.775379.

Description: Here we present Late Miocene (~11-7 Ma) model boundary conditions used by Knorr et al. [2011] in two files (Paleogeography.nc and Surface_conditions.nc). These boundary conditions relate to Figure 1 in the corresponding study. The file Paleogeography.nc (0.5°x 0.5° resolution) contains the orography (positive values and zero) and bathymetry (negative values). The file Surface_conditions.nc contains land surface conditions. Besides the glacier mask these surface conditions (3.75°x 3.75° resolution) contain the vegetation distribution that is represented by specifying different land surface parameters including, surface albedo, surface roughness length, field capacity of soil, forest ratio, leaf area index, fractional vegetation cover, and soil data flags (Food and Agriculture Organization soil map) [cf. Hagemann et al., 1999]. For further details regarding the paleogeography reconstruction and proxy-based reconstruction of the Late Miocene vegetation we would like to refer to Micheels et al. [2007], Micheels et al. [2011] and the references therein.

Description: The data files contain experimental measurements of thermal tolerance, as well as temperature-dependent development and oxygen consumption rates (i.e. thermal responsiveness) of different life stages of fish. The data were extracted from studies published between 1930 and March 2020, including marine and freshwater species from all continents and climate zones (-70° to 80° latitude). The data were analyzed to assess differences in thermal tolerance and thermal responsiveness between life stages and species living at different latitudes. A phylogenetic imputation procedure was used to predict thermal tolerance limits of life stages for which no experimental data was available. Experimental and imputed thermal tolerance data were used to estimate thermal safety margins (indicating the risk of habitat loss) of different life stages of more than 600 species under different climate change scenarios by 2100.

Description: The radiocarbon analysis of uranium-thorium-dated cold-water corals (CWCs) provides an excellent opportunity for qualitative reconstruction of past ocean circulation and water mass aging. While mid-depth water mass aging has been studied in the Atlantic Ocean, the evolution of the thermocline, tightly coupled to the atmosphere, is still largely unknown. Here we present a combined 14C and 230Th/U age record obtained from thermocline dwelling CWCs with partially centennial resolution over the last 32 ka at various locations in the central and east Atlantic Ocean (Azores Front, Mauritania, Angola), as well as in the Alboran Sea.