Description: Highlights • Sea-ice cover limits the accumulation of both coccoliths and alkenones in sediments. • Calcite dissolution in shelf sediments may explain the accumulation of alkenones in the presence of few or no coccoliths. • Non-calcifying haptophytes most likely produce alkenones in nearshore environments. Abstract We determined the abundances and concentrations of coccoliths and alkenones in 66 surface sediment samples from the northwest North Atlantic to evaluate the role that surface ocean temperature, salinity, sea-ice cover, and productivity have on the regional distribution of these two biological remains produced by haptophytes in the photic zone. In areas with sea-ice cover of more than 1 month per year, coccolith and alkenone concentrations in sediments are extremely low to nil. Elsewhere, the distribution of coccolith taxa generally displays strong relationships to water temperature, salinity, and productivity. Coccolithus pelagicus is associated with low summer sea-surface temperatures (〈8°C) and relatively high summer sea-surface salinities (〉33.5), whereas Helicosphaera carteri seems to follow the path of the North Atlantic Drift. The distribution of Emiliania huxleyi, the dominant alkenone producer, is not strongly correlated with that of alkenones. Calcite dissolution in shelf sediments could explain the occurrence of alkenones in the absence of coccoliths but alkenone production by non-calcifying haptophytes seems to also exert some control on alkenone concentrations in surface sediments, thus blurring alkenone abundance links to coccolithophorid production and their relative preservation.

Description: Limited constraints on the variability of the deep-water production in the Labrador Sea complicate reconstructions of the strength of the Atlantic Meridional Overturning Circulation (AMOC) during the Late Quaternary. Large volumes of detrital carbonates were repeatedly deposited in the Labrador Sea during the last 32 kyr, potentially affecting radiogenic Nd isotope signatures. To investigate this the Nd isotope compositions of deep and intermediate waters were extracted from the authigenic Fe-Mn oxyhydroxide fraction, foraminiferal coatings, the residual silicates and leachates of dolostone grains. We provide a first order estimation of Nd release via dissolution of detrital carbonates and its contribution to the authigenic ԑNd signatures in the Labrador Sea. During the Last Glacial Maximum the Nd isotope signatures in the Labrador Sea would allow active water mass mixing with more radiogenic ɛNd values (-12.6 and -14) prevailing in its eastern part whereas less radiogenic values (ɛNd ∼ -18.4) were found on the western Labrador slope. The deposition of detrital carbonates during Heinrich stadials (2,1) was accompanied by negative detrital and authigenic Nd isotope excursions (ɛNd ∼ -31) that were likely controlled by dissolution of dolostone or dolostone associated mineral inclusions. This highly unradiogenic signal dominated the authigenic phases and individual water masses in the Labrador Sea, serving as potential source of highly unradiogenic Nd to the North Atlantic region, while exported southward. The Holocene authigenic ɛNd signatures of the coatings and leachates significantly differed from those of the detrital silicates, approaching modern bottom water mass signatures during the Late Holocene. Key Points - Estimation of Nd release via dissolution of detrital carbonates and its contribution to the authigenic ԑNd signatures in the Labrador Sea - Dissolution of detrital dolostones in the water column during Heinrich stadials at least partially controlled ɛNd signatures - During the LGM generally more radiogenic signatures possibly indicate active water mass advection and mixing in the Labrador Sea

Description: Highlights • Porewater calcite dissolution may have occurred during the deglacial interval. • There is a significant decoupling of coccolith and alkenone concentrations in core 004. • Non-calcifying haptophytes most likely produced the alkenones in the glacial interval. Abstract The important changes that took place in the glacial cycle at the termination, from the Last Glacial Maximum to the present interglacial, deserve an examination of ocean sedimentary records that document past productivity, carbon fluxes, and carbonate preservation. In this study, we analyzed coccoliths, alkenones, and foraminifers in core HU2008–029-004 PC (61.46°N and 58.04°W, water depth = 2,674 m) from the northwestern Labrador Sea to document linkages between hydrographic conditions, biogenic carbonate fluxes to the seafloor, and their preservation/dissolution during the last 25,000 years. Large changes in coccolith and foraminifer concentrations are recorded, with sediments from the last glacial interval containing significantly less carbonate microfossils (9.5 ± 3.9 × 105 coccoliths g−1 and 2,860 ± 580 planktonic foraminifers g−1) than sediments from the deglacial and postglacial intervals (up to 3.1 × 108 coccoliths g−1 and 2.9 × 104 foraminifers g−1). Three foraminifer-based calcite dissolution indices were used to evaluate biogenic carbonate preservation: the planktonic foraminifer fragmentation index, the ratio of benthic-to-planktonic foraminifers (B/P), and the ratio of organic linings to benthic foraminifers (OL/B). Fragmentation remained low throughout the postglacial (mean of 4%) but reached up to 8% in the deglacial and peaked at 16% in samples from the Bølling-Allerød of the late glacial interval. Samples from the Bølling-Allerød and the deglacial interval also display a slightly elevated B/P index (〉0.15), which suggests that some dissolution may have occurred. In contrast, with the exception of the Bølling-Allerød and the deglacial interval, near zero OL/B values characterize most of the sequence, suggesting good biogenic carbonate preservation, which implies that the low biogenic carbonate and coccolith content in sediments of the glacial stage mirror low productivity of calcifying organisms. The elevated fragmentation of foraminifers during the Bølling-Allerød and the deglacial interval, a time of elevated productivity and low percentages of ice-rafted debris, may indicate the development of calcite undersaturated porewaters and consequent dissolution resulting from oxic remineralization of sedimentary organic matter. We also identify a significant decoupling of coccolith and alkenone concentrations throughout the core. Colder-than-expected UK37-SST estimates from the alkenones of the glacial interval rule out possible allochthonous inputs from lower-latitude locations. Instead, our records imply that at least during the glacial interval, alkenones were produced by non-calcifying haptophytes that may not follow the canonical UK37-based temperature calibrations.

Description: This dataset includes the results of the analysis of 4 marine sediment downcore records recovered from the Labrador Sea: core MD99-2227 (58° 12.38 N, 48° 22.22 W, 3460 m); core HU08-029-004 (61°27.49 N, 58°02.11 W, 2674 m); HU84-030-021 (58°22.06 N, 57°30.42 W, 2853 m); core HU91-045-094,(50°12.26 N, 45°41.14 W, 3448 m) as well as a set of surface sediment samples. Analysis includes measurement of the radiogenic Nd isotope signatures in the authigenic Fe-Mn oxyhydroxide fraction of the bulk sediment (leachates) and of the totally dissolved residual silicate (detrital) as well as analysis of uncleaned foraminifera. Data complemented by measurements of the Rare Earth Element concentrations, some major elements (Fe, Mg, Ca, Al) and radiogenic Nd isotope signatures of the dolostone grains, picked from wet-sieved 〈 63µm sediment fraction of marine sediment downcores. The downcore records were sampled with resolution of about 1 kyr and cover roughly the last 33 ka.

Description: This dataset includes the results of the analysis of a marine sediment downcore record recovered from the Labrador Sea: core HU08-029-004 (61°27.49 N, 58°02.11 W, 2674 m). Analysis includes measurement of the radiogenic Nd isotope signatures in the authigenic Fe-Mn oxyhydroxide fraction of the bulk sediment (leachates) and of the totally dissolved residual silicate (detrital) as well as analysis of uncleaned foraminifera. The downcore records were sampled with resolution of about 1 kyr and cover roughly the last 33 ka.

Description: This dataset includes the results of the analysis of a marine sediment downcore record recovered from the Labrador Sea: HU84-030-021 (58°22.06 N, 57°30.42 W, 2853 m). Analysis includes measurement of the radiogenic Nd isotope signatures in the authigenic Fe-Mn oxyhydroxide fraction of the bulk sediment (leachates) and of the totally dissolved residual silicate (detrital) as well as analysis of uncleaned foraminifera. The downcore records were sampled with resolution of about 1 kyr and cover roughly the last 33 ka.

Description: This dataset includes the results of the analysis of a marine sediment downcore record recovered from the Labrador Sea: core HU91-045-094 (50°12.26 N, 45°41.14 W, 3448 m). Analysis includes measurement of the radiogenic Nd isotope signatures in the authigenic Fe-Mn oxyhydroxide fraction of the bulk sediment (leachates) and of the totally dissolved residual silicate (detrital) as well as analysis of uncleaned foraminifera. The downcore records were sampled with resolution of about 1 kyr and cover roughly the last 33 ka.

Description: This dataset includes the results of the analysis of a marine sediment downcore record recovered from the Labrador Sea: core MD99-2227 (58° 12.38 N, 48° 22.22 W, 3460 m). Analysis includes measurement of the radiogenic Nd isotope signatures in the authigenic Fe-Mn oxyhydroxide fraction of the bulk sediment (leachates) and of the totally dissolved residual silicate (detrital) as well as analysis of uncleaned foraminifera. The downcore records were sampled with resolution of about 1 kyr and cover roughly the last 33 ka.

Description: This dataset includes the results of the analysis of 4 marine sediment downcore records recovered from the Labrador Sea: core MD99-2227 (58° 12.38 N, 48° 22.22 W, 3460 m); core HU08-029-004 (61°27.49 N, 58°02.11 W, 2674 m); HU84-030-021 (58°22.06 N, 57°30.42 W, 2853 m); core HU91-045-094,(50°12.26 N, 45°41.14 W, 3448 m). Analysis includes measurement of the radiogenic Nd isotope signatures progressively leached dolostone grains, picked from wet-sieved 〈 63µm sediment fraction of marine sediment downcores. The downcore records were sampled with resolution of about 1 kyr and cover roughly the last 33 ka.

Description: This dataset includes the results of the analysis of 4 marine sediment downcore records recovered from the Labrador Sea: core MD99-2227 (58° 12.38 N, 48° 22.22 W, 3460 m); core HU08-029-004 (61°27.49 N, 58°02.11 W, 2674 m); HU84-030-021 (58°22.06 N, 57°30.42 W, 2853 m); core HU91-045-094,(50°12.26 N, 45°41.14 W, 3448 m) as well as a set of surface sediment samples. Data contains measurements of the Rare Earth Element concentrations, some major elements (Fe, Mg, Ca, Al) and radiogenic Nd isotope signatures of the dolostone grains, picked from wet-sieved 〈 63µm sediment fraction of marine sediment downcores. The downcore records were sampled with resolution of about 1 kyr and cover roughly the last 33 ka.