Description: The changes in atmospheric pCO2 provide evidence for the release of large amounts of ancient carbon during the last deglaciation. However, the sources and mechanisms that contributed to this process remain unresolved. Here, we present evidence for substantial ancient terrestrial carbon remobilization in the Canadian Arctic following the Laurentide Ice Sheet retreat. Glacial-retreat-induced physical erosion of bedrock has mobilized petrogenic carbon, as revealed by sedimentary records of radiocarbon dates and thermal maturity of organic carbon from the Canadian Beaufort Sea. Additionally, coastal erosion during the meltwater pulses 1a and 1b has remobilized pre-aged carbon from permafrost. Assuming extensive petrogenic organic carbon oxidation during the glacial retreat, a model-based assessment suggests that the combined processes have contributed 12 ppm to the deglacial CO2 rise. Our findings suggest potentially positive climate feedback of ice-sheet retreat by accelerating terrestrial organic carbon remobilization and subsequent oxidation during the glacial-interglacial transition.

Description: Holocene sea ice and palaeoenvironmental conditions were reconstructed using three sediment cores from northeastern Baffin Bay (GeoB19948-3 and GeoB19927-3) and the Labrador Sea (GeoB19905-1) along a north-south transect based on sea ice IP25 and open-water phytoplankton biomarkers (brassicasterol, dinosterol and HBI III). In Baffin Bay, sea-surface conditions in the Early Holocene were characterized by extended (early) spring sea ice cover (SIC) prior to 7.6 ka BP. The conditions in the NE Labrador Sea, however, remained predominantly ice-free in spring/autumn due to the enhanced influx of Atlantic Water (i.e., WGC; West Greenland Current) from 11.5 to ~9.1 ka BP, succeeded by a period of continued (spring-autumn) ice-free conditions from 9.1 to 7.6 ka BP corresponding to the onset of Holocene Thermal Maximum (HTM)-like conditions. A transition towards reoccurring ice-edge and significantly reduced SIC conditions in Baffin Bay is evident in the Mid Holocene (~7.6-3 ka BP) probably caused by the variations in the WGC influence associated with the ice melting and can be characterized as HTM-like conditions. These HTM-like conditions are predominantly recorded in the NE Labrador Sea area shown by (spring-autumn) ice-free conditions from 5.9-3 ka BP. In the Late Holocene (last ~3 ka), our combined proxy records from eastern Baffin Bay indicate low in-situ ice-algae production, however, enhanced multi-year (drifted) sea ice in this area was possibly attributed to the increased influx of Polar Water mass influx and may correlate with the Neoglacial cooling. The conditions in the NE Labrador Sea during the last 3 ka, however, continued to remain (spring-autumn) ice-free with decreased biological carbonate production probably linked to decreased WGC strength and/or increased Arctic Water influx, coinciding with the Neoglacial cooling.

Description: The data originates from the gravity core MSM12/2-5-1 (57.538500, -48.738700, recovery 1494 cm, 3492 m water depth) taken during R/V Maria S. Merian cruise MSM12/2 in 2009 in the eastern Labrador Sea (Eirik Drift). The data should provide more precise information on the timing and duration of freshwater forcing, which may help to improve simulations for past and future changes in ocean circulation and climate. We have investigated the very well-dated and high-resolution sediment core from the Eirik Drift, representing an interval from the last deglaciation to Holocene, i.e., the last 19 ka. Four meltwater-related cold events have been identified by abrupt changes in sea surface characteristics, which are based on independent multiple biomarker proxies, including sea-ice proxy IP25 and phytoplankton biomarker IP25 index (PIP25) for sea ice cover, the alkenone unsaturation index for sea surface temperature (SST), and the percentage of tetra-unsaturated alkenones (%C37:4) for meltwater inflow, and X-ray fluorescence (XRF) scanning data. Furthermore, sortable silt mean size has been used to reflect changes in bottom current intensity. In conclusion, our study could improve our understanding of the impact of meltwater injection into subpolar regions on abrupt climate changes during the last glacial termination. Furthermore, the data support modelling results that higher frequency and amplitude of abrupt changes may occur during the transition states from background climates. We found that meltwater pulses following collapse of the Laurentide Ice Sheet and/or Greenland Ice Sheet might have triggered millennial-scale abrupt changes in surface freshening and sea ice concentrations in the Labrador Sea, as well as cooling atmospheric temperatures.

Description: Sea ice and paleoenvironmental conditions were reconstructed based on gravity core MSM45_19-2 from the northern Labrador Shelf. Gravity core MSM45_19-2 was obtained during R/V Maria S. Merian expedition MSM45 (58°45.68'N, 61°56.25'W, water depth: 202 m) in 2015 (Schneider et al., 2016). For paleoenvironmental reconstructions of the last 9,000 years BP, biomarkers representing sea ice algae productivity (IP25), open-water phytoplankton productivity (brassicasterol, dinosterol and HBI III (Z)) and terrigenous input (campesterol) where analyzed. Aim of this study was to investigate (i) the role sea ice played before and during the final demise of the Laurentide Ice Sheet between 8.7 and 8.2 kyr BP, and (ii) the effects of meltwater events on remaining sea-ice cover and primary productivity. Concentrations of specific biomarkers were analyzed. 4-5 g of each sediment sample were extracted by sonication (3 x 15 min) using dichloromethane:methanol (2:1 v/v; 30 ml) as solvent. Prior to biomarker extraction two internal standards 7-HND (7-hexylnonadecane, 20 μl/sample) and androstanol (5α-androstan-3β-ol, 20 μl/sample) were added for quantification purposes. Hydrocarbon and sterol fractions were separated by open-column chromatography with SiO2 as stationary phase. For hydrocarbons, n-hexane (5 ml) and for sterols, ethylacetate:n-hexane (2:8 v/v; 7 ml) were used as eluent. Sterol fractions were silylated using 200 μl BSTFA (2 h, 60°C). Hydrocarbon concentrations were determined with a gas chromatograph coupled to an mass selective detector. For detailed measurement settings and compound identification see Fahl and Stein (2012). All biomarker concentrations were normalized to both the extracted weight of sediment (μg/gSed) and TOC (μg/gTOC). Further, accumulation rates were calculated (μg/cm2/yr) after the following equation (e.g., Stein & Macdonal, 2004): MAR = SR x DBD(1) TOC AR = MAR x TOC/100(2) BM AR = MAR x BM(3) with MAR = Marine Accumulation Rate, SR = sedimentation rate (cm/yr), DBD = dry buld density (g/cm3), TOC = total organic carbon, BM = biomarker concentration (μg/gSed), AR = accumulation rate. Equation (2) was also applied to calculate BSi accumulation rates. After the determination of biomarker concentrations, the PIP25 index was calculated as follows: PIP25 = IP25/(IP25 + (PM x c))(4) with PM = phytoplankton marker (brassicasterol (PBIP25), dinosterol (PDIP25) or HBI III (Z) (PIIIIP25)) and c = balance factor. The balance factor c is the ratio of mean IP25 concentration and mean sterol concentration, counterbalancing generally higher concentrations of sterols compared to IP25. As HBI III (Z) and IP25 showed similar concentrations in the initial studies from the Barents Sea lead to the assumption that the use of the balance factor c unnecessary in the calculation of the PIIIIP25 index (Belt et al., 2015; Smik et al., 2016).

Description: Total Organic Carbon (TOC) concentrations were measured as indicator for past primary productivity on gravity core MSM45_19-2 from the northern Labrador Shelf. Gravity core MSM45_19-2 was obtained during R/V Maria S. Merian expedition MSM45 (58°45.68'N, 61°56.25'W, water depth: 202 m) in 2015 (Schneider et al., 2016). Dry Bulk Density (DBD) was calculated based on sample volume and water content and later used to calculate Marine Accumulation Rates (MAR). The total organic carbon (TOC) content was analyzed (using ELTRA, CS-800) on freeze-dried and homogenized sediment samples, after the removal of carbonates by hydrochloric acid (37%, 500 μl).