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The size of the last glacial ice sheet on the Northeast (NE) Greenland shelf and its interaction with ocean circulation have been the subject of debate. Here we provide insights into the extent of the ice sheet around the Last Glacial Maximum (LGM) and investigate timing and strength of changes in the flow of Atlantic Water. The study is based on a multiproxy investigation of a marine sediment core, gravity core DA17-NG-ST01-019G, from 323-m water depth at the NE Greenland shelf edge at 79.4°N. We present benthic and planktic foraminiferal distribution data, AMS-14C dates, sedimentological (ice-rafted debris (IRD) and grain sizes), and geochemical (XRF) data in combination with geophysical (sub-bottom profiler) data. The oldest sediments at the study site are dated to 25.5–17.5 ka, encompassing the time frame from the beginning of the LGM to the early deglaciation. This part is overlain by sediments from the late deglaciation and Holocene. The deposits dating from the LGM are very rich in both planktic and benthic foraminifera and macrofossils of excellent preservation. The faunas show that the site generally was affected by a strong flow of relatively warm subsurface Atlantic Water during the LGM and Early Holocene. Conditions turned more polar with cold bottom water flow in the Middle–Late Holocene (c. 7.5 ka to Recent) with presence of mainly agglutinated benthic foraminiferal species. Our data from the LGM also indicate that the deposits were mixed by iceberg scouring, confirmed by the geophysical data showing extensive ploughing of the sediments on the outer shelf area. The results further indicate that the Greenland Ice Sheet did not reach to the edge of the NE Greenland shelf at 79.4°N during the LGM 24–18 ka.

The western Fram Strait is the only deep-water gateway connecting the Arctic Ocean and North Atlantic. Consequently, today, the western Fram Strait and the Northeast Greenland shelf receive cold, low saline Polar and Arctic Atlantic waters from the Arctic Ocean incorporated in the East Greenland Current, together with warmer, saline recirculated Atlantic Water masses derived from the West Spitsbergen Current. We present a multiproxy study (grain size distribution, XRF core scans, and benthic foraminiferal assemblages) based on the lower part of the radiocarbon dated marine sediment core DA17-NG-ST03-039G, covering the period from 13.3 to 3.9 cal ka BP. We reconstruct the deglacial conditions of the Northeast Greenland shelf together with Early to Mid Holocene fluctuations in subsurface Atlantic Water and Polar Water advection. The results show that the outer Northeast Greenland shelf was deglaciated and marine conditions were established prior to c. 13.3 cal ka BP. At this time, our data show Atlantic Water masses flowing beneath an extensive sea-ice cover in a glaciomarine setting, potentially related to the Bølling-Allerød warm period. Around 12.9 cal ka BP, the onset of high surface and bottom water productivity may be associated with the Younger Dryas onset. This was followed by a transition towards warmer bottom and subsurface water conditions from c. 11.7 until 10.2 cal ka BP caused by enhanced advection of Atlantic-derived water masses. A cold period with marginal ice zone conditions and enhanced East Greenland Current incursion is evident from 10.2 to 9.4 cal ka BP, succeeded by harsher sea-ice conditions and Atlantic Water inflow, prevailing until c. 7.5 cal ka BP. Holocene Thermal Maximum conditions, characterized by high surface and subsurface water productivity, were promoted by enhanced Atlantic Water flow to the shelf from c. 7.5 to 6.7 cal ka BP. In contrast, the transition towards a cold period with increased drift-ice transport via a strong East Greenland Current is recorded from c. 6.2 cal ka BP and to the end of our record at 3.9 cal ka BP; it was associated with the onset of the Neoglaciation., Quaternary Science Reviews, 293, ISSN:0277-3791

The Fram Strait is one of the largest gateways through which meltwater and sea ice are exported to thesubarctic North Atlantic, transiting the North-East Greenland shelf via the southward flowing EastGreenland Current. Observations indicate a recent freshening of the East Greenland Current that mayhave implications for wider oceanic circulation regimes. The North-East Greenland shelf is an opportuneregion to assess these changes back through time. Paleoceanographic reconstructions from the North-East Greenland shelf are sparse and their temporal coverage is limited to the Holocene, limiting ourability to assess the impact of rapid climatic variations on marine conditions, such as during the YoungerDryas/Holocene transition. Here, we present data from a well-dated marine sediment core retrieved fromthe North-East Greenland shelf (74N; east of Young Sound-Tyrolerfjord system) that captures the lateYounger Dryas Stadial through to the Mid-Holocene at sub-centennial resolution. We apply a multi-proxyapproach to reconstruct changes in productivity, surface and bottom ocean conditions. We show that at74 N the presence of warm Atlantic waters on the inner North-East Greenland shelf was limited to thelate Younger Dryas, as the Greenland Ice Sheet retreated landward and isostatic rebound caused the areato uplift. A unique dimension to this record is its location within one of the few biological hotspots on theEast Greenland shelf today; the Sirius Water polynya. Archaeological studies indicate the polynya wasforming as early as 4500 years ago, but nothing is known about its evolution from a marine perspective.Cooling of bottom waters, increasing sea-surface productivity and more frequent open water conditionsindicate an Early Holocene onset of the Sirius Water (ca. 10e8.7 ka BP).

The melting of marine terminating glaciers in Northeast Greenland is a visible sign that our climate is changing. This melt has been partly attributed to changes in oceanic heat fluxes, particularly warming of Atlantic Water (AW). Yet our understanding of the interaction between glaciers and the ocean is limited by the length of instrumental records. Here, we present a multi-proxy study (benthic foraminifera assemblages, CT scans, grain size, XRF, and stable isotope data) on core DA17-NG-ST08-092G, located 90 km east of the Northeast Greenland Ice Stream (NEGIS). Whilst the exact timing of deglaciation is uncertain, it is certain to have occurred at least as early as 12.5 ka cal BP, and likely before 13.4 ka cal BP. The inflow of AW may have played a role in the seemingly early deglaciation on the Northeast Greenland continental shelf. Following deglaciation, the site was overlain by an ice shelf, with AW and Polar Water (PW) flowing beneath until 11.2 ka cal BP. The NEGIS briefly retreated westwards between 11.2 and 10.8 ka cal BP before our site returned to glacier-proximal conditions dominated by colder subsurface water and persistent AW flowing beneath (10.8–9.6 ka cal BP). Between 9.6 and 7.9 ka cal BP the NEGIS retreated westwards; there was a continued presence of AW and PW at the site. A drastic shift in ocean circulation occurred at 7.9 ka cal BP, with a decline in AW flow and dominance of PW flowing beneath perennial sea ice. During the Late Holocene, there was return of AW and likely breakup of perennial sea ice., Quaternary Science Reviews, 286, ISSN:0277-3791

The timing of the flooding of the Danish/German/Swedish straits and the first marine influence in the Baltic Basin after the Ancylus Lake stage has been much debated. Here we present 47 new radiocarbon ages from sediment cores retrieved from Danish waters, ages that record the marine transgression of the area. Most of the ages are based on shells of marine molluscs, hence the ages are uncertain because we do not know the precise reservoir age in the past.We use a reservoir age of 400 years, which is based on dating of museum specimens collected live before testing of nuclear bombs. It appears from the ages that the Great Belt (Storebælt) was inundated before The Sound (Øresund). The oldest ages on marine shells from the northern part of the Great Belt region are about 8.9 cal. ka BP.From the central part of the Great Belt, the oldest ages are about 8.2 cal. ka BP, in Mecklenburg Bay 8.1 cal. ka BP and in the Arkona Basin 7.1 cal. ka BP. Sediments deposited prior to the occurrence of marine molluscs contain brackish-water ostracods (Cyprideis torosa and Cytheromorpha fuscata); the sediments are usually laminated and non-bioturbated mud. The brackish-water phase may have lasted 500–1000 years. The youngest lake deposits without signs of marine influence are dated to c. 8.8 cal. ka BP(central Great Belt), 8.7 cal. ka BP(Little Belt)and8.5 cal. ka BP(Arkona Basin). We see no evidence for marine influence at c. 10 cal. ka BP as recorded by some studies from the Baltic Basin.

We address here the specific timing and amplitude of sea-surface conditions and productivity changes off SW Greenland, northern Labrador Sea, in response to the high deglacial meltwater rates, the Early Holocene maximum insolation and Neoglacial cooling. Dinocyst assemblages from sediment cores collected off Nuuk were used to set up quantitative records of sea ice cover, seasonal sea-surface temperature (SST), salinity (SSS), and primary productivity, with a centennial to millennial scale resolution. Until similar to 10 ka BP, ice-proximal conditions are suggested by the quasi-exclusive dominance of heterotrophic taxa and low dinocyst concentrations. At about 10 ka BP, an increase in species diversity and abundance of phototrophic taxa marks the onset of interglacial conditions at a regional scale, with summer SST reaching up to 10 degrees C between 8 and 5 ka BP, thus in phase with the Holocene Thermal Maximum as recorded in the southern Greenlandic areas/northern Labrador Sea. During this interval, low SSS but high productivity prevailed in response to high meltwater discharge and nutrient inputs from the Greenland Ice Sheet. After similar to 5 ka BP, a decrease in phototrophic taxa marks a two-step cooling of surface waters. The first started at similar to 5 ka BP, and the second at similar to 3 ka BP, with a shift toward colder conditions and higher SSS suggesting reduced meltwater discharge during the Neoglacial. This second step coincides with the disappearance of the Saqqaq culture. The gap in human occupation in west Greenland, between the Dorset and the Norse settlements from 2000 to 1000 years BP, might be linked to high amplitude and high frequency variability of ocean and climate conditions.

A new calcareous Arctic foraminiferal species, Glomulina oculus n. sp., belonging to the suborder Miliolina has been observed in surface samples from northern Nares Strait and Petermann Fjord, NW Greenland, and off Zachariae Isbrae, NE Greenland, as well as in early Holocene sediments from the northern Baffin Bay region and on the NE Greenland shelf. In some samples, this new porcelaneous species makes up a significant fraction of the foraminiferal assemblage, particularly in samples with a relatively large sand content, and we suggest that this species is indicative of an Arctic environment with marine-terminating glaciers. Yet, further studies are needed to ascertain its full habitat range.

We propose a new relative shore-level curve for the Aarhus Bugt area, an embayment in eastern Jylland, Denmark, based on a compilation of pub- lished and new radiocarbon ages of organic material. Lakes existed in the area during the Late Glacial and Early Holocene. Lake level rose gradually until the region was inundated by the sea at c. 9000 cal. years BP. The relative sea level reached a high stand at about 6000 cal. years BP, when the local relative sea level was c. 3 m above present-day mean sea level. The Aarhus Bugt area was inundated by the sea later than the Limfjord area in northern Jylland, but earlier than the Lillebælt region in southern Denmark. The shore- level curves for these areas differ partly because the glacio-isostatic uplift was more pronounced in the Limfjord area than farther south and partly because the northern regions were inundated by the sea earlier than the southern areas.

The Labrador Current is part of the anticlockwise subpolar gyre and plays a major role in the formation of North Atlantic Deep Water. It is influenced by the West Greenland and Baffin currents supplying warmer Atlantic and cold polar waters, respectively. During the early Holocene, at the final stage of the last deglaciation, meltwater and iceberg discharge caused highly variable conditions in the Labrador Current. In order to assess its sensitivity to such freshening, this study provides a well-resolved Holocene paleoclimatic record from the Labrador Shelf. Based on benthic foraminiferal faunal and alkenone biomarker analyses, we differentiated four distinct climatic periods in the western Labrador Sea. From 8.9 to 8.6 ka BP, the Labrador Shelf was dominated by polar water outflow from Baffin Bay and covered by perennial sea ice. Between 8.6 and 7.4 ka BP, a strong subsurface inflow of warmer Atlantic water masses is ascribed to an intensification and redirection of the West Greenland Current. At 7.4 ka BP, the decreased influence of Atlantic water masses on the Labrador Shelf marks the establishment of winter convection leading to the formation of Labrador Sea Water in the central basin. Concurrently, an intensified polar water outflow through the Canadian Gateways strengthened the inner Labrador Current, and higher primary productivity suggests longer spring blooms because of a shorter sea-ice season during the Holocene Thermal Maximum. In the late Holocene after 3 ka BP, periodic fluctuations of primary productivity may tentatively be correlated with stronger and weaker northwesterly winds.

The polar regions exhibit some of the most visible signs of climate change globally; annual mass loss from the Greenland Ice Sheet (GrIS) has quadrupled in recent decades, from 51 ± 65 Gt yr−1 (1992-2001) to 211 ± 37 Gt yr−1 (2002-2011). This can partly be attributed to the widespread retreat and speed-up of marine-terminating glaciers. The Zachariae Isstrøm (ZI) is an outlet glacier of the Northeast Greenland Ice Steam (NEGIS), one of the largest ice streams of the GrIS (700km), draining approximately 12% of the ice sheet interior. Observations show that the ZI began accelerating in 2000, resulting in the collapse of the floating ice shelf between 2002 and 2003. By 2014, the ice shelf extended over an area of 52km2, a 95% decrease in area since 2002, where it extended over 1040km2. Paleo-reconstructions provide an opportunity to extend observational records in order to understand the oceanic and climatic processes governing the position of the grounding zone of marine terminating glaciers and the extent of floating ice shelves. Such datasets are thus necessary if we are to constrain the impact of future climate change projections on the Arctic cryosphere.A multi-proxy approach, involving grain size, geochemical, foraminiferal and sedimentary analysis was applied to marine sediment core DA17-NG-ST8-92G, collected offshore of the ZI, on the Northeast Greenland Shelf. The aim was to reconstruct changes in the extent of the ZI and the palaeoceanographic conditions throughout the Early to Mid Holocene (c.a. 12,500-5,000 cal. yrs. BP). Evidence from the analysis of these datasets indicates that whilst there has been no grounded ice at the site over the last 12,500 years, the ice shelf of the ZI extended as a floating ice shelf over the site between 12,500 and 9,200 cal. yrs. BP, with the grounding line further inland from our study site. This was followed by a retreat in the ice shelf extent during the Holocene Thermal Maximum; this was likely to have been governed, in part, by basal melting driven by Atlantic Water (AW) recirculated from Svalbard or from the Arctic Ocean. Evidence from benthic foraminifera suggest that there was a shift from the dominance of AW to Polar Water at around 7,500 cal. yrs. BP, although the ice shelf did not expand again despite of this cooling of subsurface waters.

Arctic sea ice is declining at an unprecedented pace as the Arctic Ocean heads towards ice-free summers within the next few decades. Because of the role of sea ice in the Earth System such as ocean circulation and ecosystem functioning, reconstructing its past variability is of great importance providing insight into past climate patterns and future climate scenarios. Today, much of our knowledge of past sea-ice variability derives from a relatively few microfossil and biogeochemical tracers, which have limitations, such as preservation biases and low taxonomic resolution. Marine sedimentary ancient DNA (marine sedaDNA) has the potential to capture more of the arctic marine biodiversity compared to other approaches. However, little is known about how well past communities are represented in marine sedaDNA. The transport and fate of DNA derived from sea-ice associated organisms, from surface waters to the seafloor and its eventual incorporation into marine sediment records is poorly understood. Here, we present results from a study applying a combination of methods to examine modern and ancient DNA to material collected along the Northeast Greenland Shelf. We characterized the vertical export of genetic material by amplicon sequencing the hyper-variable V4 region of the 18S rDNA at three water depths, in surface sediments, and in a dated sediment core. The amplicon sequencing approach, as currently applied, includes some limitations for quantitative reconstructions of past changes such as primer competition, PCR errors, and variation of gene copy numbers across different taxa. For these reasons we quantified amplicons from a single species, the circum-polar sea ice dinoflagellate Polarella glacialis in the marine sedaDNA, using digital droplet PCR. The results will increase our understanding on the taphonomy of DNA in sea ice environments, how sedimentation differs among taxonomic groups, and provide indications to potentially useful marine sedaDNA-based proxies for climate and environmental reconstructions.

The Last Glacial Maximum (LGM, 23–19,000 year BP) designates a period of extensive glacial extent and very cold conditions on the Northern Hemisphere. The strength of ocean circulation during this period has been highly debated. Based on investigations of two marine sediment cores from the Davis Strait (1033 m water depth) and the northern Labrador Sea (2381 m), we demonstrate a significant influx of Atlantic-sourced water at both subsurface and intermediate depths during the LGM. Although surface-water conditions were cold and sea-ice loaded, the lower strata of the (proto) West Greenland Current carried a significant Atlantic (Irminger Sea-derived) Water signal, while at the deeper site the sea floor was swept by a water mass comparable with present Northeast Atlantic Deep Water. The persistent influx of these Atlantic-sourced waters entrained by boundary currents off SW Greenland demonstrates an active Atlantic Meridional Overturning Circulation during the LGM. Immediately after the LGM, deglaciation was characterized by a prominent deep-water ventilation event and potentially Labrador Sea Water formation, presumably related to brine formation and/or hyperpycnal meltwater flows. This was followed by a major re-arrangement of deep-water masses most likely linked to increased overflow at the Greenland-Scotland Ridge after ca 15 kyr BP.

In recent decades the surface water temperature and salinity in the Labrador Sea have been influenced by atmospheric circulation patterns, such as the North Atlantic Oscillation (NAO), as well as a trend to increasingly warm atmospheric temperatures in recent years. These changes are concerning, given the important role that temperature and salinity have on deep convection in the Labrador Sea. Yet, due to the shortness of available records, the long-term patterns of climate variability in the region are not clear. Here, a diatom-based reconstruction of summer sea-surface temperature (SST) developed from Trinity Bay, Newfoundland, provides insight into variations of SST since 7.2 cal ka BP in the southwestern Labrador Sea. The results show that the Holocene Thermal Maximum (HTM) lasted until c. 5.2 cal ka BP, which was followed by a gradual cooling trend overprinted by centennial temperature fluctuations of 1–2°C. Long-term cooling was likely the result of declining Northern Hemisphere orbital summer insolation, potentially amplified by long-term changes in surface and bottom water salinity, which led to a gradual reduction in the stratification of the water column. Centennial fluctuations in temperature vary in-phase with reconstructed variations in the NAO, supporting a consistent relationship between atmospheric circulation and SST over centennial-millennial timescales. Other factors influencing the SST variability may have been solar forcing during the mid-Holocene and variations in the strength of the subpolar gyre during the late-Holocene. The most prolonged cool period at 5.2–4.1 cal ka BP coincides with sharply reduced salinity in the Labrador Sea and a weakening of deep ventilation in the northeast Atlantic, highlighting a period with altered ocean surface conditions and circulation across the northern North Atlantic.

Four marine sediment cores from two sites in the Independence Fjord system near the Wandel Sea in eastern North Greenland were analyzed for their dinoflagellate cyst (dinocyst) and foraminiferal fossil content to gain insight into the water mass properties and evolution of the outer fjord system over the Holocene and Last Glacial Period. While regarded as a climate-sensitive region, the climatic history of the area remains largely unknown and has been documented through the study of two composite marine sediment cores only once before. The results presented here reveal that Atlantic waters entered the Independence Fjord episodically during the studied interval. High concentrations of dinocysts and foraminifers in the upper few centimeters of the cores are in line with oceanographic measurements clearly illustrating that Atlantic-sourced waters make up the lower part of the water column in the area in modern times. Radiocarbon dating of foraminiferal tests and increasing microfossil concentrations and diversity toward the top of the cores suggest that this inflow has been occurring for at least 2,000 years and intensified toward recent times. The core sections below the upper few centimeters are devoid of (Quaternary) dinocysts and calcareous foraminifera with the exception of the lowermost segments of the longer cores. While low foraminiferal test quantities in these lowermost core sections prevent precise age determination, their radiocarbon ages reveal that they were deposited prior to 30,000 years ago, indicating the existence of a pathway for the occasional intrusion of Atlantic-sourced waters into, and thus relatively small local ice caps around, the fjord system prior to the Last Glacial Maximum. The previously documented early Holocene inflow of Atlantic-sourced waters was not detected in our records, likely suggesting a strong topographical and deglacial control on the routing of these water masses during the early Holocene.

Through a process called “bioturbation,” burrowing macrofauna have altered the seafloor habitat and modified global carbon cycling since the Cambrian. However, the impact of macrofauna on the community structure of microorganisms is poorly understood. Here, we show that microbial communities across bioturbated, but geochemically and sedimentologically divergent, continental margin sites are highly similar but differ clearly from those in nonbioturbated surface and underlying subsurface sediments. Solid- and solute-phase geochemical analyses combined with modeled bioturbation activities reveal that dissolved O2 introduction by burrow ventilation is the major driver of archaeal community structure. By contrast, solid-phase reworking, which regulates the distribution of fresh, algal organic matter, is the main control of bacterial community structure. In nonbioturbated surface sediments and in subsurface sediments, bacterial and archaeal communities are more divergent between locations and appear mainly driven by site-specific differences in organic carbon sources., Proceedings of the National Academy of Sciences of the United States of America, 117 (27), ISSN:0027-8424, ISSN:1091-6490

Baffin Bay is a semi-enclosed basin connecting the Arctic Ocean and the western North Atlantic, thus making out a significant pathway for heat exchange. Here we reconstruct the alternating advection of relatively warmer and saline Atlantic waters versus the incursion of colder Arctic water masses entering Baffin Bay through the multiple gateways in the Canadian Arctic Archipelago and the Nares Strait during the Holocene. We carried out benthic foraminiferal assemblage analyses, X-ray fluorescence scanning, and radiocarbon dating of a 738 cm long marine sediment core retrieved from eastern Baffin Bay near Upernavik, Greenland (Core AMD14-204C; 987 m water depth). Results reveal that eastern Baffin Bay was subjected to several oceanographic changes during the last 9.2 kyr. Waning deglacial conditions with enhanced meltwater influxes and an extensive sea-ice cover prevailed in eastern Baffin Bay from 9.2 to 7.9 ka. A transition towards bottom water amelioration is recorded at 7.9 ka by increased advection of Atlantic water masses, encompassing the Holocene Thermal Maximum. A cold period with growing sea-ice cover at 6.7 ka interrupts the overall warm subsurface water conditions, promoted by a weaker northward flow of Atlantic waters. The onset of the neoglaciation at ca. 2.9 ka is marked by an abrupt transition towards a benthic fauna dominated by agglutinated species, likely in part explained by a reduction of the influx of Atlantic Water, allowing an increased influx of the cold, corrosive Baffin Bay Deep Water originating from the Arctic Ocean to enter Baffin Bay through the Nares Strait. These cold subsurface water conditions persisted throughout the Late Holocene, only interrupted by short-lived warmings superimposed on this cooling trend.

The Arctic region exhibits some of the most visible signs of climate change globally. Arctic sea ice extent and volume has been declining sharply in recent decades; observations indicate a mean annual decrease of 3.2% since 1980. However, no extensive network of sea ice observations extends back further than the mid-18th century and satellite data since the late 1970s; this limits perspectives of sea ice variability on longer time scales. Thus, to understand the processes governing sea-ice cover and variability, predict how sea ice and ocean conditions will respond to anthropogenic climate change and to understand if the shrinking of Arctic sea ice is a unique and irreversible process, longer records of sea ice variability and oceanic conditions are required.A multi-proxy approach, involving grain size, geochemical, foraminifera and sedimentary analysis, was applied to a marine sediment core from North East Greenland to reconstruct changes in sea ice extent and palaeoceanographic conditions throughout the early Holocene (ca. 12,400-7,800 cal. yrs. BP). The study aimed to improve the understanding of the interaction between ocean circulation, sea ice and fluctuations of the Zachariae Isstrøm (ZI), one of the main glacier outlets of NE Greenland. Four distinct zones have been identified: Zone 1 (12,400-11,600 cal. yrs. BP) covering the transition from the Younger Dryas into the Holocene which evidences a gradually warming climate, resulting in a retreat of the ZI; Zone 2 (11,600 – 10,300 cal. yrs. BP) which encapsulates two distinct cooling events as a result of cooler surface waters, rapid release of freshwater and local feedback mechanisms. This coincides with sudden re-advances of the ZI followed by gradual retreats; 3) Zone 3 (10,300 – 8,600 cal. yrs. BP) shows warm and stable conditions, with warm surface waters that resulted in the retreat of the ZI; 4) Zone 4 (8,600 – 7,800 cal. yrs. BP) which shows a rapid return to cooler conditions, with cold surface waters and rapid freshwater outbursts resulting in the re-advance of the ZI, forced by decreasing solar insolation and cold surface waters. Our investigation thus indicated that changes in oceanic conditions at the NE Greenland shelf had a significant impact on the extent and melting rate of the ZI glacier.

Knowledge of the impact of past climate warming on Greenland Ice Sheet stability is an important issue for assessing thresholds that are critical for a potential ice sheet collapse. For the late Holocene, evidence has recently been found of a so-called 4.2 ka BP event(1) including a prominent warming spike in several ice core records from Greenland and Canada (Agassiz). Also lake records from both Northwest(2) and South Greenland(3) support pronounced summer warming during that time. After c. 4.0 ka BP NW Greenland July air temperature dropped by about 3o C. Coeval with this exceptional atmospheric warming anomaly over northern Canada and parts of Greenland, abrupt cooling and freshening affected the N-Atlantic subpolar gyre where Labrador Sea deep convection ceased(4). Northern N-Atlantic climate generally deteriorated. With our contribution we present Holocene sub-bottom profiling and sedimentary shelf and fjord records from Southwest Greenland and Disko Bay that indicate exceptional Greenland Ice Sheet melting 4.4-4.0 ka BP at a rate and magnitude not recorded since early Holocene deglaciation. Extremely strong melt water discharge resulted in erosion of fjord sediments(5) and local deposition of up to several meters thick meltwater sediment on the shelf(6-8). Timing of this melting event corresponds to a significant anomaly in hydrographic parameters of the Labrador Current off Newfoundland(9,10), which is concluded to have resulted in thermohaline perturbation of the N-Atlantic Subpolar gyre. (1) Weiss, H. 2019. Clim Past doi:10.5194/cp-2018-162-RC2 (2) McFarlin, J.M. et al. 2018. PNAS doi:10.1073/pnas.1720420115 (3) Andresen, C.S. et al. 2004. J Quat Sci 19(8) doi:10.1002/jqs.886 (4) Klus, A. et al. 2018. Clim Past doi:10.5194/cp-14-1165-2018 (5) Ren, J. et al. 2009. Mar Micropal doi:10.1016/j.marmicro.2008.12.003 (6) Hygom Jacobsen, S. 2019. Master Thesis Aarhus Univ, Dept. of Geoscience, pp105 (7) Schneider, R. 2015. Cruise Rep epic.awi.de/id/eprint/37062/131/msm-44-46-expeditionsheft.pdf (8) Kuijpers, A. et al. 2001. Geol. Greenland Surv Bull 189, 41-47 (9) Solignac, S. et al. 2011. The Holocene, doi: 10.1177/0959683610385720 (10) Orme, L. et al 2019. The Holocene (submitted)

As we move towards a “blue” Arctic Ocean in the summer within the next decades, predicting the full range of effects of climate change on the marine arctic environment remains a challenge. This is partly due to the paucity of long-term data on ocean-biosphere-cryosphere interactions over time and partly because, today, much of our knowledge on past ocean variability derives from microfossil and biogeochemical tracers that all have considerable limitations such as preservation biases and low taxonomic resolution or coverage.Recent studies have revealed sedaDNA as a potential “game-changer” in our ability to reconstruct past ocean conditions, due to the preservation of DNA at low temperatures, and the possibility to capture a much larger fraction of the Arctic marine biome diversity than with classical approaches. However, while sedaDNA has been used in terrestrial, archeological, and lake studies for some years, its application to marine sediment records is still in its infancy.Here, we will present new results from material recently collected along the two Arctic Ocean outflow shelves off Greenland (Greenland Sea/Fram Strait and Northern Baffin Bay/Nares Strait). We have used a combination of modern and ancient DNA methods applied to seawater, surface sediments, and sediment cores covering the past ca. 12 000 years with the objectives of: 1) characterizing the vertical export of sea ice-associated genetic material through the water column and into the sediments following sea ice melt and 2) exploring the potential of sedaDNA from the circum-polar sea ice dinoflagellate Polarella glacialis as a new sea ice proxy. For the first objective, we followed a comparative metabarcoding approach while the second objective included designing species-specific primers followed by gene copy number quantification by a droplet digital PCR assay. We argue that sedaDNA will have a critical role in expanding the Paleoceanography “toolbox” and lead to the establishment of a new cross-disciplinary field.

The chemical composition of foraminiferal calcite is widely used for studying past environmental conditions and biogeochemistry. However, high rate of microbial-derived organic matter degradation and abundant dissolved metal sources in sediment and pore waters may impede the application of paleoenvironmental proxies due to formation of secondary carbonates on the outside and/or inside of foraminiferal tests. Secondary carbonate precipitation severely alters the foraminiferal geochemistry and can be difficult to eliminate through standard cleaning procedures for foraminiferal trace element analyses. Here we present results of the mineral composition and formation sequence of diagenetic coatings on the tests of foraminifera formed under extreme anoxic conditions in the Baltic Sea deepest basin (the Landsort Deep, IODP Exp. 347, Site M0063), as well as changing trace element concentrations of authigenic carbonates on the test on a millennial time-scale. The focus is on the diagenetic carbonates present on the tests of the low-oxygen tolerant benthic foraminiferal species Elphidium selseyensis and Elphidium clavatum. We applied geochemical and imaging methods by using scanning electron microscope imaging (SEM) and energy dispersive spectroscopy (EDS), synchrotron-based x-ray fluorescence microscopy (nano-XRF), RAMAN spectroscopy and laser ablation (LA)-ICP-MS, in order to ascertain the sedimentary diagenetic processes, and the foraminiferal authigenic mineral formation sequence. The authigenic carbonates were enriched in Mg, Mn, Fe and Ba, depending on the redox environmental conditions when the authigenic carbonates were precipitated. In particular, concentrations of redox-sensitive elements such as Mn and Fe were increased in bottom waters and sedimentary pore waters under oxygen-depleted conditions in the Landsort Deep, which resulted in Mn- and Fe-enriched carbonate formation. The diagenetic alteration on foraminiferal tests provides potential opportunity to investigate past sedimentary redox environment and primary productivity in the Baltic Sea.

The chemical composition of foraminiferal calcite is widely used for studying past environmental conditions and biogeochemistry. However, high rates of microbial organic matter degradation and abundant dissolved metal sources in sediments and pore waters may impede the application of foraminifera-based proxies due to formation of secondary carbonates or other authigenic minerals on and/or inside of foraminiferal tests. Secondary carbonate precipitation severely alters the bulk foraminiferal geochemistry and can be difficult to eliminate through standard foraminiferal trace element cleaning procedures. We present results showing the mineral composition and formation sequence of diagenetic coatings on foraminiferal tests formed under extreme anoxic conditions in the Baltic Sea's deepest basin (the Landsort Deep, IODP Exp. 347, Site M0063). Our study focuses primarily on the diagenetic carbonates present on and in the tests of the low-oxygen tolerant benthic foraminiferal species Elphidium selseyensis and Elphidium clavatum. We applied various geochemical and imaging methods to ascertain the diagenesis processes and the authigenic mineral formation sequence on foraminifera. The authigenic carbonates were enriched in Mn, Mg, Fe and Ba, depending on the environmental redox conditions when the authigenic carbonates were precipitated. Concentrations of redox-sensitive elements such as Mn and Fe were particularly elevated in bottom waters and sedimentary pore waters under oxygen-depleted conditions in the Landsort Deep, resulting in formation of carbonates with highly elevated Mn and Fe contents. In addition to Mn- and Fe carbonates, several other types of authigenic minerals also formed on and in the foraminiferal chambers, including authigenic calcite, and non-carbonate accessory minerals. The formation sequence reveals the redox sensitivities of different elements and the preferential sequence of oxidants used by the microbes during organic matter oxidation and secondary redox reactions. This study provides a case study of extreme early diagenesis of foraminiferal calcite and may serve as a valuable guide when interpreting foraminiferal trace element records from low oxygen environments.

The East Asian winter monsoon (EAWM) significantly impacts living conditions in a large part of Asia, and therefore, it is important to understand its major driving mechanisms. Winter sea surface temperature (SSTW) and circulation in the southern Okinawa Trough are today both primarily controlled by the EAWM. Here we present a new SSTW reconstruction for the last millennium based on a diatom record from sediment core MD05-2908, from the continental slope of the southern Okinawa Trough off northeastern Taiwan. Our reconstruction indicates that SSTW varied between 14.1 and 19.6°C over the past 1,000 years. Changes in SSTW in the southern Okinawa Trough correspond closely to the index of warm winters based on historical documents from the East Asian monsoon domain. This implies that our SSTW record can be used to reconstruct EAWM variability during the last millennium. Comparisons with the reconstructed winter Arctic Oscillation (AO, developed from historical snow anomaly events in Eastern Asia) and Arctic sea ice cover reveal a significant positive correlation between the EAWM and AO during the time interval from 1000–1400 Common Era (C.E.), coinciding with reduced sea ice cover. However, there is no significant correlation with increased sea ice cover during the interval from 1400 to 1700 C.E. This suggests that the reduction in Arctic sea ice may periodically have played a role in strengthening the relationship between the EAWM and the AO during the last millennium and that the current and future reduction in Arctic sea ice may have significant consequences for the EAWM.

Climate during the Last Interglacial period (LIG, Marine Isotope Stage 5e) was on average warmer than the present, with a higher global sea level but also more unstable conditions. Today, the Baltic Sea interacts strongly with conditions in the North Atlantic region, and this interaction was likely even stronger during the LIG. We here present a reconstruction of seawater conditions during the LIG based on benthic foraminiferal geochemistry (stable isotopes and trace elements) and compare these records with modern marine monitoring data to evaluate seasonal hydrographic conditions in the western and southern Baltic Sea during the first half of the LIG (130–123 ka BP). Our reconstructions reflect the evolution of seasonal temperature and salinity, rather than annual mean conditions. The spring LIG bottom water temperatures in the Skagerrak and Kattegat were ∼2–3 °C higher compared to the modern spring bottom water temperatures. During the LIG, there was an increase in seasonality in bottom water temperature (progressively warmer summers and cooler springs) in the southern Baltic Sea, which can be linked to seasonal insolation changes. Moreover, our data suggest a decreased gradient of bottom water salinity along a transect through the Skagerrak-Kattegat-Danish Straits-southern Baltic Sea, supporting previous investigations inferring a stronger ocean-water influx into the Baltic Sea during the LIG than at present.

We present a reconstruction of Holocene sea-ice variability from sediment core GA306-GC3, from the Holsteinsborg Dyb off West Greenland, which provides an index of palaeoceanographic and palaeoenvironmental conditions within this climatically sensitive region during the last 6700 yr. The reconstructed sea-ice record, combined with previously published proxy data, suggests that relatively warm conditions with reduced sea-ice extent prior to 5000 cal. yr BP were associated with the Holocene Thermal Maximum. Subsequent cooling and extensive sea-ice cover between ca. 5000 and 4000 cal. yr BP was followed by even colder conditions and persistent sea-ice cover during the Neoglacial cooling phase, particularly after ca. 1500 cal. yr BP. There is a positive correlation between West Greenland sea-ice cover and solar activity over the past 5000 yr, but the correlation is much weaker prior to 5000 cal. yr BP. In addition, there is a strong link between West Greenland sea ice and changes in the abundance of arctic benthic foraminifera species, related to different water masses of the West Greenland Current during the entire interval, even prior to 5000 cal. yr BP. Our findings indicate that sea-ice variability off West Greenland was driven not only by solar activity, but also by ocean circulation (the strength of cold Polar water from the East Greenland Current and warm Atlantic water from the Irminger Current).

Using qualitative and quantitative analyses of planktonic foraminifera assemblages, δ18O measurements, Mg/Ca–temperature relationship ( Globigerinoides ruber pink sensu stricto) data and sea-surface temperatures (SSTs) derived from artificial neural network (ANN) transfer functions, a reconstruction was made of upper water mass variability in the Anegada–Jungfern Passage (AJP), northeastern Caribbean Sea, over the last c. 11,100 years. Our record is based on the study of two marine sediment cores and reveals three main circulation stages during the Holocene. In the early-Holocene (11,100–6300 cal. yr BP), ANN-based SST estimations indicate moderately cooler than present winter condition in the NE Caribbean with SSTs of ~25.5°C. These conditions presumably reflect advection of well-mixed upper water masses from the Guyana upwelling area associated with a strong Atlantic Meridional Overturning Circulation (AMOC) and enhanced trade wind activity, linked to a more northerly location of the inter-tropical convergence zone (ITCZ). Between 6300 and 3700 cal. yr BP, a relative warming of winter SSTs (~26.5°C) was probably related to a weaker circulation and upper water mass mixing because of less intense trade wind activity, as the ITCZ moved southwards. From 3700 cal. yr BP to the present, the region was characterised by small seasonal SST variations and generally stable winter and summer SSTs. The data suggest a minor shift in the (sub)surface inflow pattern during the last 2000 years, possibly related to changes in Northern Hemisphere large-scale atmospheric circulation also observed at higher latitude. The ANN-based temperature pattern is supported by fluctuations in the Mg/Ca-derived temperature record, although temperature maxima derived from the Mg/Ca ratio appear anomalously high. On a Holocene timescale, we conclude that the northeastern Caribbean SST and circulation regime have been mainly dependent on the position of the ITCZ, which, in turn, is controlled by changes in hemispheric solar insolation.

We here reconstruct a glacial and climate history of arctic NW Siberia for the last ~600,000 years, based on the stratigraphy and chronology of 35 studied river sections on the southern Taimyr Peninsula. From this stratigraphic mosaic we have identified four glacial events, marked by tills/glaciotectonics, which are intercalated with mainly marine sediments deposited in proglacial settings during transitions from glacial conditions into subsequent interglacials/interstadials. The traces of early shelf-based Kara Sea Ice Sheet (KSIS) glaciations in marine isotope stages (MIS) 12–14 and 8 are sparsely preserved, but these ice advances are suggested to have terminated far south into the central Siberian uplands, as also was the case with the younger Taz glaciation (MIS 6). The inception phase of the latter glaciation was complex, with ice advancing into a proglacial marine basin both from the south (Putorana – Anabar uplands) and the north. The deglaciation leading into the Karginsky interglacial (MIS 5e) was marked by the development of the southernmost ice-marginal zones (IMZs) on the Taimyr lowlands – the Urdakh and Sampesa IMZs. The most recent (late Pleistocene) glacial cycle is recorded by three successively smaller KSIS advances from the Kara Sea shelf onto Taimyr, of which only the first, during Early Zyryanka (MIS 5d), reached south of the Byrranga Mountains, with its maximum extent marked by the Jangoda – Syntabul – Severokokorsky IMZ. Retreat of the ice margin during MIS 5c-b was accompanied by deposition of glaciomarine sediment in the proglacial basin and deposition of large successions of delta sediments in the foothills of the Byrranga Mountains, reaching ≥100 m above present sea level. The region north of the Byrranga Mountains was subjected to two subsequent KSIS glaciations, during MIS 4 and MIS 2, while the area south of the Byrranga Mountains transitioned to a terrestrial environment from the Middle into the Lower Zyryanka, as evidenced by deposition of fluvial, aeolian and ice-complex (Yedoma) sediments.

This Data in Brief paper contains data (including images) from Quaternary sedimentary successions investigated along the Bol'shaya Balakhnya River and the Luktakh–Upper Taimyra–Logata river system on southern Taimyr Peninsula, NW Siberia (Russia). Marine foraminifera and mollusc fauna composition, extracted from sediment samples, is presented. The chronology (time of deposition) of the sediment successions is reconstructed from three dating methods; (i) radiocarbon dating of organic detritus (from lacustrine/fluvial sediment) and molluscs (marine sediment) as finite ages (usually 42 000–48 000 years) on samples/sediments beyond the radiocarbon dating limit; (ii) Electron Spin Resonance (ESR) dating on marine molluscs (up to ages >400 000 years); (iii) Optically Stimulated Luminescence (OSL) dating, usually effective up to 100–150 0000 years. Terrestrial Cosmogenic Nuclide (TCN) exposure dating has been applied to boulders resting on top of moraine ridges (Ice Marginal Zones). See (Möller et al., 2019) (doi.org/10.1016/j.earscirev.2019.04.004) for interpretation and discussion of all data. Keywords: Taimyr, Glacial sedimentology, Glacial history, Kara Sea ice sheet, OSL dating, ESR dating, TCN dating

This paper presents new marine evidence of Lateglacial and Holocene environmental changes in the western part of Limfjorden, and provides a review of the geological history/development of this part of northern Jylland, Denmark. Lateglacial clay without fossils is widespread in the region and is probably a glaciolacustrine deposit. Limfjorden began to form as a strait in the Early Holocene due to rising relative sea level and the oldest marine shells are dated to c. 9300 cal. years BP. We propose a new relative sealevel curve for the region based on new and published data, which appear to confirm that the relative sea-level change was not extremely rapid, which was suggested earlier. During the Mid-Holocene a wide connection existed from the western part of Limfjorden to the North Sea in the west and more narrow connections existed between Limfjorden and Skagerrak in the north. The marine fauna included several species that indicate warmer and more salty waters than at present. Gradually, the connections to the North Sea and Skagerrak closed due to long-shore sediment transport and deposition of aeolian sand combined with a fall in the relative sea level during the Middle- to Late Holocene. During the Viking Age, 800–1050 CE (Common Era), the western connection to the North Sea was still open, but around 1200 CE it was closed by a coastal sandy barrier and the western part of Limfjorden became brackish. The coastal barrier was flooded on several occasions but soon formed again. After 1825 CE the western connection from Limfjorden to the North Sea has been maintained artificially.

Although geological and modelling evidence indicate that the last glacial inception in North America was in NE Canada, little is known about the glacial response of the nearby western Greenland Ice Sheet (GIS) during the glacial advance of marine oxygen isotope stage 4 (MIS4). Our multi-proxy study of a marine sediment core collected about 60 km southwest of the Outer Hellefisk Moraines demonstrates that in the southern Davis Strait region the most extreme Greenland shelf glaciation of the last glacial cycle occurred during MIS 4, with another prominent glacial advance at 37–33 kyr BP. During those periods the GIS likely reached the Outer Hellefisk Moraines in this area. Except for these two periods, our data suggest significant advection of relatively warm Irminger Sea Water by the West Greenland Current since MIS 4. This advection likely limited the extent of the MIS2 glaciation on the SW Greenland shelf. Decreased precipitation over southwestern Greenland predicted by atmospheric models as a downstream effect of a much larger MIS2 Laurentide Ice Sheet may have played an additional role.

The mass loss from the Greenland Ice Sheet has increased over the past 2 decades. Marine-terminating glaciers contribute significantly to this mass loss due to increased melting and ice discharge. Periods of rapid retreat of these tidewater glaciers have been linked to the concurrent inflow of warm Atlantic-sourced waters. However, little is known about the variability of these Atlantic-derived waters within the fjords, due to a lack of multi-annual in situ measurements. Thus, to better understand the potential role of ocean warming on glacier retreat, reconstructions that characterize the variability of Atlantic water inflow to the fjords are required. Here, we investigate foraminiferal assemblages in a sediment core from Upernavik Fjord, West Greenland, in which the major ice stream Upernavik Isstrøm terminates. We conclude that the foraminiferal assemblage is predominantly controlled by changes in bottom water composition and provide a reconstruction of Atlantic water inflow to Upernavik Fjord, spanning the period 1925–2012. This reconstruction reveals peak Atlantic water influx during the 1930s and again after 2000, a pattern that is comparable to the Atlantic Multidecadal Oscillation (AMO). The comparison of these results to historical observations of front positions of Upernavik Isstrøm reveals that inflow of warm Atlantic-derived waters likely contributed to high retreat rates in the 1930s and after 2000. However, moderate retreat rates of Upernavik Isstrøm also prevailed in the 1960s and 1970s, showing that glacier retreat continued despite a reduced Atlantic water inflow, albeit at a lower rate. Considering the link between bottom water variability and the AMO in Upernavik Fjord, and the fact that a persistent negative phase of the AMO is expected for the next decade, Atlantic water inflow into the fjord may decrease in the coming decade, potentially minimizing or stabilizing the retreat of Upernavik Isstrøm during this time interval.

Benthic foraminiferal populations were studied in a shallow bay of San Salvador Island, the Bahamas. Surface sediments and marine macrophytes were collected from 14 sample sites along a 500 m transect at Grahams Harbour to investigate the foraminiferal assemblage in each microhabitat and to test the link between dead foraminiferal test accumulation patterns and living epiphytic and sedimentary foraminiferal assemblages, macrophyte distribution, and environmental gradients. The analyses include grain size measurements, macrophyte biomass quantification, and qualitative and quantitative studies of benthic foraminifera. The foraminifera found attached to macrophytes differed between macrophyte habitats. However, a correlation between these living communities and the dead assemblages in the sediments at the same sites could not be observed. Principal component analysis (PCA) and redundancy analysis (RDA) suggest that the presence of the macroalgae Halimeda explains 16 % of the residual faunal variation in the dead foraminiferal assemblage after the effects of sorting according to fall speed are partialled out. The RDA also reflects a positive correlation between foraminifera larger than 1.0 mm in diameter and the 0.25–0.5 mm sediment grain size, indicating sedimentological processes as the main factor controlling the sedimentary epiphytic foraminiferal assemblages. These sedimentary processes overprint most effects of ecological features or macrophyte-specific association.

Pockmarks or crater-like depressions formed due to fluid venting, is a well-known geological phenomenon. On a global scale, pockmarks expel a significant amount of fluids and greenhouse gasses to the marine environment and the atmosphere. Despite pockmarks being well-studied, the longevity and history of activity are rarely addressed. In this study, we analyse more than twenty nearshore seafloor depressions of varying morphology and size in the shallow waters of the western Limfjord in northern Denmark. By using high-resolution seismo-acoustic and sediment core data, we characterize the morphology and sediments of the pockmarks. We further use 14C-dating and pore water analyses to address the timing and activity of the depressions. Our results show that the depressions coincide with submarine groundwater discharge areas and hence represent freshwater pockmarks. The pockmarks most likely formed initially due to two eruptive events of thermogenic light oil/gas ca. 2000 and 900 yrs. BP, both triggered by relative sea-level fall. Freshwater seepage continues to sustain and develop the pockmark morphology and we show that pockmarks grow by collapse of pockmark walls and amalgamation of discrete erosive seepage sites at the bottom. The episodic expulsions of thermogenic fluids and the continuous seepage of freshwater probably prolonged the longevity of the studied pockmarks and further demonstrates the complex nature of pockmark formation and activity. While thermogenic and biogenic gas escape to the surface, on the global scale, is relevant for the greenhouse gas budget, the outflow of groundwater which may or may not be polluted is relevant with respect to the geochemistry, biota and productivity of the receiving marine environment especially in shallow water settings.

Evaluating and understanding bio-environmental relationships at different spatial and temporal scales is important for accurately assessing marine productivity in relation to oceanographic conditions in changing Arctic ecosystems. In this paper, we compare four different bio-environmental datasets, in order to shed new light on the complex marine ecosystem of the Baffin Bay-Labrador Sea region, as well as the historical links between environmental changes and the ecosystem. Satellite dataset was used to describe the regional distribution of chlorophyll a, sea ice concentration (SIC), sea surface temperature (SST) and sea surface salinity (SSS). Chlorophyll a data were also analysed together with shrimp assessment dataset to examine the relationship between marine pelagic productivity and bottom feeders off the Greenland coast. A microfossil dataset (diatom valves) from 57 surface sediment stations was used to describe diatom concentration and diversity across the study region. It was also used in combination with satellite data from the same sites to analyse species-environment relationships and develop a diatom-based transfer function for reconstructing past changes in SIC, SST and SSS. Subsequently, we applied the diatom transfer function on three short sediment cores from off SW and W Greenland spanning the last few centuries. A monitoring dataset of sea ice observations and instrumental measurements of water temperature and salinity, together with atmospheric data (air temperature and wind conditions) from Greenland, were used to develop a more complete picture of 20th and 21st century changes in ocean-climate conditions. Our comparative analyses show clear spatial distribution patterns of marine phytoplankton and identify key ecological groups linked to oceanic conditions. In addition, we find a significant correlation between the different trophic levels, culminating in a ‘productivity boom’ in 2001 CE. On a longer temporal scale, the transfer function reconstructions reveal a good correlation with the satellite, monitoring and observational trends, as well as a consistent, long-term decrease in sea ice linked to ocean-climate variability.

Arctic sea ice represents an important component of the climate system, and the present reduction of sea ice in the Arctic is of major concern. Despite its importance, little is known about past changes in sea-ice cover and the underlying forcing mechanisms. Here, we use diatom assemblages from a marine sediment core collected from the West Greenland shelf to reconstruct changes in sea-ice cover over the last millennium. The proxy-based reconstruction demonstrates a generally strong link between changes in sea-ice cover and solar variability during the last millennium. Weaker (or stronger) solar forcing may result in the increase (or decrease) in sea-ice cover west of Greenland. In addition, model simulations show that variations in solar activity not only affect local sea-ice formation, but also control the sea-ice transport from the Arctic Ocean through a sea-ice–ocean–atmosphere feedback mechanism. The role of solar forcing, however, appears to have been more ambiguous during an interval around AD 1500, after the transition from the Medieval Climate Anomaly to the Little Ice Age, likely to be driven by a range of factors.

Late- and postglacial geological evolution of the southern Kattegat connection to the Great Belt was investigated from high-resolution seismic data and radiocarbon-dated sediment cores in order to elucidate the Ancylus Lake drainage/Littorina Sea transgression. It was found that glacial deposits form the acoustic basement and are covered by Lateglacial (LG) marine sediments and postglacial (PG; Holocene) material. The LG deposits form a highstand systems tract, whereas the PG deposits cover a full depositional sequence, consisting of a lowstand systems tract (PG I), transgressive systems tract (PG II; subdivided into three parasequences) and finally a highstand systems tract (PG III). PG I sand deposits (11.7–10.8 cal. ka BP) are found in a major western channel and in a secondary eastern channel. PG II (10.8–9.8 cal. ka BP) consists of estuarine and coastal deposits linked to an estuary located at the mouth of the channels. Both channels drained fresh water from south to north. The PG III, that is younger than 9.8 cal. ka BP, represents the threshold marine flooding at the southeastern branch of the palaeo-Great Belt channel. At 9.3 cal. ka BP, fully marine conditions were established, shortly before the flooding of the threshold to the northern part of the Great Belt. These early Holocene spits and sand bars are preserved as features on the present seabed, probably as a result of the rapid sea-level rise that led to back-stepping of the early Holocene palaeo-coast system. This study shows no evidence of major erosion or delta deposition linked to the emptying of the Ancylus Lake, which suggests that continuous water flow from the south characterized the area, without any major drainage event of the Ancylus Lake impacting the southwestern Kattegat.

The last deglaciation was marked by intervals of rapid climatic fluctuations accompanied by glacial advances and retreats along the eastern margin of the Laurentide Ice Sheet. One of these climatic events, the Younger Dryas cold reversal, was accompanied by a detrital carbonate event referred to as “Heinrich event 0” (H0) that deposited ice-rafted debris and especially detrital carbonate-rich (DC) sediment layers in the western and southern Labrador Sea. The precise age, duration, source, and geographical distribution of the H0 DC event, however, are not entirely clear. A high-sedimentation rate sequence cored off southern Newfoundland yielded an age of ~11.5–11.3 calibrated kyr B.P. for this layer, thus pointing to its deposition directly following the Younger Dryas termination, likely associated with rapid ice retreat and warming at the onset of the Holocene. At the study site, the H0 layer contains increased concentrations of detrital carbonates (calcite/dolomite ratio ~ 2.5:1) and a mature biomarker composition, similar to that found in Heinrich Layers 1, 2, 4, and 5, which together suggest an origin from Hudson Strait. Grain size analysis indicates that the H0-sediments were transported to the study site mostly through shallow plumes along the Labrador Shelf, with some hyperpycnal dispersal, deeper, along the slope and rise. Our data thus point to a large meltwater release caused by retreat of the ice margin in the Hudson Strait area. The relvatively short duration of the H0 layer, and its timing right after a major climatic transition, combined with its ubiquitous regional occurrence makes it valuable for correlating different sediment records from the western Labrador Sea.

International audience; The Last Interglacial (LIG) represents an invaluable case study to investigate the response of components of the Earth system to global warming. However, the scarcity of absolute age constraints in most archives leads to extensive use of various stratigraphic alignments to different reference chronologies. This feature sets limitations to the accuracy of the stratigraphic assignment of the climatic sequence of events across the globe during the LIG. Here, we review the strengths and limitations of the methods that are commonly used to date or develop chronologies in various climatic archives for the time span (∼140–100 ka) encompassing the penultimate deglaciation, the LIG and the glacial inception. Climatic hypotheses underlying record alignment strategies and the interpretation of tracers are explicitly described. Quantitative estimates of the associated absolute and relative age uncertainties are provided.Recommendations are subsequently formulated on how best to define absolute and relative chronologies. Future climato-stratigraphic alignments should provide (1) a clear statement of climate hypotheses involved, (2) a detailed understanding of environmental parameters controlling selected tracers and (3) a careful evaluation of the synchronicity of aligned paleoclimatic records. We underscore the need to (1) systematically report quantitative estimates of relative and absolute age uncertainties, (2) assess the coherence of chronologies when comparing different records, and (3) integrate these uncertainties in paleoclimatic interpretations and comparisons with climate simulations.Finally, we provide a sequence of major climatic events with associated age uncertainties for the period 140–105 ka, which should serve as a new benchmark to disentangle mechanisms of the Earth system's response to orbital forcing and evaluate transient climate simulations.

Palynomorph and foraminiferal assemblages have been studied from the Upper Pliensbachian to Bathonian of a borehole section on the island of Anholt in the Kattegat, situated near the eastern margin of the Norwegian-Danish Basin. Palynomorphs were recorded throughout the succession and have been used for both biostratigraphical and palaeoenvironmental assessments. Foraminifera were recorded from only the lower part of the succession, where they proved useful for interpreting palaeoenvironments. Four palynomorph and three foraminiferal zones have been established.The interval encompasses a palaeoenvironmental transition from a marine, inner shelf setting to mainly terrestrial conditions. The Upper Pliensbachian-Toarcian boundary marks the beginning of a major regression, which continued through the Toarcian and Aalenian. Hence, it took place significantly earlier at Anholt than in the centre of the Norwegian-Danish Basin, where a lowering of sea level did not occur until the late Toarcian.The Jurassic succession on Anholt spans the Fjerritslev and Haldager Sand formations; biostratigraphical data indicate that the Lower-Middle Jurassic boundary is here located within the uppermost part of the Fjerritslev Formation. The Fjerritslev and Haldager Sand formational transition was previously considered to coincide with the Lower-Middle Jurassic boundary.

Rising global sea level caused by melting ice sheets poses a major challenge ina persistently warming climate. The Greenland Ice Sheet (GrIS) is among the maincontributors, and in order to make accurate predictions of future ice retreat and sealevel rise, it is imperative to understand how the ice sheet responded to global warming in the past. Reconstructions of relative sea level (RSL) are a key constraint in models of past ice sheet fluctuations, however, high-precision data has until now been sparse in North Greenland. In this study, we present a RSL reconstruction for Finderup Land, North Greenland based on five isolation lakes located between 19.6 and 81.2 m a.s.l. The transition between marine and lacustrine sediments has been identified using XRF, lithological interpretation, and foraminiferal analysis. Age constraints are based on 14C dating of foraminifera and paleomagnetic age correlation. Our results show that Finderup Land was ice free by 10.8 0.2 cal ka BP with a subsequent rapid RSL fall occurring from 9.5 0.2 to 8.0 cal ka BP, at which point the RSL started to approach present level. Furthermore, we establish the marine limit to be minimum at 81.2 m a.s.l. We compare our data to modeled RSL predictions for the area and our results indicate a faster RSL fall, which in turn reflects that the ice retreat was more rapid than estimated and possibly, that the ice sheet in North and Northeast Greenland was larger than previous estimates suggest.

Dinoflagellate cyst assemblages in a marine sediment core from the Iceland Basin were used to carry out qualitative and quantitative assessments of upper ocean conditions in the northern branch of the Subpolar Gyre (SPG) during the Holocene. The data revealed that the early Holocene, i.e. prior to similar to 6.8 kyr B.P., experienced elevated summer sea surface temperatures (SST). In contrast, winter SST was lower compared to modern conditions. This stronger-than-present seasonality revealed by our data thus shows the influence of the early Holocene insolation forcing. Higher seasonality also dominated the reconstructed sea surface salinity (SSS) in the same period, with lower salinity during both summers and winters. The lower SSS suggests freshwater advection into the SPG, and the dinoflagellate cyst content from this interval indicates a dominant sourcing from the Canadian Labrador coast, and thus the eastern margin of the Laurentide Ice Sheet. Within this interval of low SSS, the onset of the Holocene Climate Optimum stands out by its distinct "marine" assemblage components and associated high summer SST and relative SSS increase between 9.3 and 7.8 kyr B.P. A prominent shift in the overall assemblage composition occurs at 6.8 kyr B.P., with lower seasonality in sea surface conditions from that time onwards. Increased summer and winter SSS suggest that this change is linked to the halted influence of meltwater from the Laurentide Ice Sheet, a westward shift of the subpolar front and a contracted SPG allowing an easier northward movement of southern-sourced North Atlantic waters, contributing to and consequently sustained by the spin-up of the overturning circulation. The subpolar front appears to gradually have moved slightly eastward again between 2.8 and 1.9 kyr B.P. towards its modern-day position, with a subtle increase of elements characterized by a typical East Greenland Current signature in the Iceland Basin. Finally, spectral analyses indicate that a range of periodicities may be present in the new SSS and SST records, most notably a 2000-yr periodicity in SSS changes, although none of the periodicities are dominant in both records or throughout the time interval covered by the records.

An edited version of this paper was published by AGU. Copyright 2018 American Geophysical Union. Limoges, A., Ribeiro, S., Weckström, K., Heikkilä, M., Zamelczyk, K., Andersen, T.J, ... Seidenkrantz, M. (2018). Linking the modern distribution of biogenic proxies in High Arctic Greenland shelf sediments to sea ice, primary production and Arctic-Atlantic inflow. Journal of Geophysical Research: Biogeosciences, 123(3), 760-786. https://doi.org/10.1002/2017JG003840. To view the published open abstract, go to https://doi.org/10.1002/2017JG003840. The eastern north coast of Greenland is considered to be highly sensitive to the ongoing Arctic warming, but there is a general lack of data on modern conditions and in particular on the modern distribution of climate and environmental proxies to provide a baseline and context for studies on past variability. Here we present a detailed investigation of 11 biogenic proxies preserved in surface sediments from the remote High Arctic Wandel Sea shelf, the entrance to the Independence, Hagen, and Danmark fjords. The composition of organic matter (organic carbon, C:N ratios, δ13C, δ15N, biogenic silica, and IP25) and microfossil assemblages revealed an overall low primary production dominated by benthic diatoms, especially at the shallow sites. While the benthic and planktic foraminiferal assemblages underline the intrusion of chilled Atlantic waters into the deeper parts of the study area, the distribution of organic‐walled dinoflagellate cysts is controlled by the local bathymetry and sea ice conditions. The distribution of the dinoflagellate cyst Polarella glacialis matches that of seasonal sea ice and the specific biomarker IP25, highlighting the potential of this species for paleo sea ice studies. The information inferred from our multiproxy study has important implications for the interpretation of the biogenic‐proxy signal preserved in sediments from circum‐Arctic fjords and shelf regions and can serve as a baseline for future studies. This is the first study of its kind in this area.

Atmospheric circulation may change with future climate change in response to modification of meridional temperature gradients, but the potential influence on ocean circulation is as yet unclear. Over the mid-late Holocene, atmospheric circulation in the North Atlantic region has fluctuated on millennial timescales; therefore, the ocean response to these changes can be investigated using the paleoceanographic records that have been developed in the north-eastern subpolar North Atlantic. Here, we present a diatom-based sea surface temperature reconstruction from the Iceland Basin, south of Iceland; the reconstruction shows the warmest temperatures of the record at 6.1–4 ka BP, cooler temperatures at 4-2 ka BP and warmer temperatures thereafter. Inter-record comparisons indicate that the cold period at c. 4-2 ka BP may have resulted from a strengthened East Greenland Current and/or melting of the Greenland ice sheet, in response to a negative North Atlantic Oscillation. The findings highlight that atmospheric circulation changes are likely to cause pronounced variations in the latitudinal exchange of heat, which may have consequences for deep-water formation and global ocean circulation.

Benthic foraminiferal assemblages supported by selected geochemical data from three marine sediment cores collected in Placentia Bay, SE Newfoundland, are used to construct an ~13,000-year-long record of regional oceanographic changes in the SW Labrador Sea. The area is located in the boundary zone between the cold, ice-loaded Labrador Current (LC) in the north and the warm Gulf Stream (GS) waters to the south. After the Younger Dryas termination, the influence of GS-derived water increased and was further strengthened at 10.7 cal. kyr BP through enhanced northward flow of Atlantic water via the Slopewater Current. A short-term event of increased terrestrial input and water column stratification at 8.4 cal. kyr BP was likely linked to the distal drainage of glacial Lake Agassiz. After 7.3 cal. kyr BP, a stronger LC weakened the inflow of warmer subsurface waters from the GS. This may be explained by extensive meltwater release from ice sheets in Arctic Canada and is concurrent with a general shift in oceanographic conditions in the Labrador Sea region. Around 4.0 cal. kyr BP, conditions became more stable with a slight increase in salinity, indicating a decrease in meltwater transported via the LC. The Northern Hemisphere neoglacial cooling around 2.8 cal. kyr BP was characterized off SE Newfoundland by a further stabilization of the current system, dominated by the LC with some continued influx of GS water.

Mounting evidence from proxy records suggests that variations in solar activity have played a significant role in triggering past climate changes. However, the mechanisms for sun-climate links remain a topic of debate. Here we present a high-resolution summer sea-surface temperature (SST) record covering the past 9300 yr from a site located at the present-day boundary between polar and Atlantic surface-water masses. The record is age constrained via the identification of 15 independently dated tephra markers from terrestrial archives, circumventing marine reservoir age variability problems. Our results indicate a close link between solar activity and SSTs in the northern North Atlantic during the past 4000 yr; they suggest that the climate system in this area is more susceptible to the influence of solar variations during cool periods with less vigorous ocean circulation. Furthermore, the high-resolution SST record indicates that climate in the North Atlantic regions follows solar activity variations on multidecadal to centennial time scales.

Køge Bugt, in southeast Greenland, hosts three of the largest glaciers of the Greenland Ice Sheet; these have been major contributors to ice loss in the last two decades. Despite its importance, the Holocene history of this area has not been investigated. We present a 9100 year sediment core record of glaciological and oceanographic changes from analysis of foraminiferal assemblages, the abundance of ice-rafted debris, and sortable silt grain size data. Results show that ice-rafted debris accumulated constantly throughout the core; this demonstrates that glaciers in Køge Bugt remained in tidewater settings throughout the last 9100 years. This observation constrains maximum Holocene glacier retreat here to less than 6 km from present-day positions. Retreat was minimal despite oceanic and climatic conditions during the early-Holocene that were at least as warm as the present-day. The limited Holocene retreat of glaciers in Køge Bugt was controlled by the subglacial topography of the area; the steeply sloping bed allowed glaciers here to stabilise during retreat. These findings underscore the need to account for individual glacier geometry when predicting future behaviour. We anticipate that glaciers in Køge Bugt will remain in stable configurations in the near-future, despite the predicted continuation of atmospheric and oceanic warming.

Source at https://doi.org/10.1007/s13280-016-0894-2. In order to establish a baseline for proxy-based reconstructions for the Young Sound–Tyrolerfjord system (Northeast Greenland), we analysed the spatial distribution of primary production and sea ice proxies in surface sediments from the fjord, against monitoring data from the Greenland Ecosystem Monitoring Programme. Clear spatial gradients in organic carbon and biogenic silica contents reflected marine influence, nutrient availability and river-induced turbidity, in good agreement with in situ measurements. The sea ice proxy IPz25 was detected at all sites but at low concentrations, indicating that IP25 records from fjords need to be carefully considered and not directly compared to marine settings. The sea ice-associated biomarker HBI III revealed an open-water signature, with highest concentrations near the mid-July ice edge. This proxy evaluation is an important step towards reliable palaeoenvironmental reconstructions that will, ultimately, contribute to better predictions for this High Arctic ecosystem in a warming climate.