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We combine geomorphological and sediment core evidence to investigate phases of ice margin stability and instability during retreat of the Boothia Lancaster Ice Stream (BLIS) of the NE Laurentide Ice Sheet (LIS) since the Last Glacial Maximum (LGM). Sediment cores 2008029-059 PC and TWC (59CC) and 2013029-064 PC (64 PC) from Lancaster Sound and Baffin Bay, respectively, represent LGM through Holocene environments, including three Baffin Bay Detrital Carbonate (BBDC) events that have been thought to manifest calving events within Lancaster Sound. Previous mapping of glacigenic landforms shows that 64 PC lies within the LGM limit of the convergent BLIS and Tasiujaq Ice Stream (TIS) on the northeastern Baffin Island shelf, while 59CC terminates within subglacial/ice marginal sediments termed the Baffin Shelf Drift (BSD), capturing the history of BLIS retreat from 15.3 cal ka BP onward. In 64 PC, a basal sediment gravity flow deposit is overlain by dolomite-rich BBDC 2, which is re-interpreted here as a subglacial/ice marginal deposit and renamed GZ-BBDC. Both gravity flows are interpreted to have formed during retreat of the confluent TIS and BLIS from the LGM maximum extent. Overlying GZ-BBDC, in 64 PC, is a finely laminated lithofacies interpreted as an ice-shelf facies formed beneath the ice shelf fronting the confluent TIS and BLIS when it occupied a large LGM grounding zone wedge (GZW) in northern Baffin Bay. The ice-shelf facies indicates temporary stabilization of the conjoined TIS and BLIS. The overlying thin black glaciomarine diamicton records disintegration of the ice shelf and retreat of the TIS. Ice retreat over Cretaceous and younger bedrock into Lancaster Sound is recorded by dark brown diamicton and glaciomarine sediments in 59CC. The overlying tan, detrital carbonate-rich glaciomarine diamicton, BBDC 1 in 59 PC, manifests calving retreat of the BLIS onto the Paleozoic carbonate bedrock within Lancaster Sound by 15 cal ka BP. A slightly later onset of BBDC 1 in 64 PC, of ca.14.5 cal ka BP, points to the influence of local conditions such as sea ice and local iceberg calving on the distribution of IRD off of Pond Inlet. The pause in ice rafting and detrital carbonate deposition between BBDC 1 and BBDC 0 within the Younger Dryas chron likely results from BLIS readvance to Devon Island and its stabilization there until 11.6 cal ka BP. BLIS retreat into Prince Regent Inlet marks the onset of BBDC 0. These new results indicate multiple periods of instability of the BLIS, which are responsible for BBDC events identified throughout Baffin Bay. 

ABSTRACT Glacial marine sediment deposition varies both spatially and temporally, but nearly all studies evaluate down-core (∼ time) variations in sediment variables with little consideration for across core variability, or even the consistency of a data set over distance scales of 1 to 1000 m. Grain size and quantitative X-ray diffraction (qXRD) methods require only ≤ 1 g of sediment and thus analyses assume that the identification of coarse sand (i.e., ice-rafted debris) and sediment mineral composition are representative of the depth intervals. This assumption was tested for grain size and mineral weight % on core MD99-2317, off East Greenland. Samples were taken from two sections of the core that had contrasting coarse-sand content. A total of fourteen samples were taken consisting of seven (vertical) and two (horizontal) samples, with five replicates per sample for qXRD analyses and ∼ 10 to 20 replicates for grain size. They had an average dry weight of 10.5 ± 0.5 g and are compared with two previous sets of sediment samples that averaged 54.1 ± 18.9 g and 20.77 ± 5.8 g dry weight. The results indicated some significant differences between the pairs of samples for grain-size parameters (mean sortable silt, and median grain size) but little difference in the estimates of mineral weight percentages. Out of 84 paired mineral and grain-size comparisons only 17 were significantly different at p = < 0.05 in the post-hoc Scheffe test, all of which were linked to grain-size attributes. 

Abstract. The North Water Polynya (NOW, Inuktitut: Sarvarjuaq; Kalaallisut:Pikialasorsuaq), Baffin Bay, is the largest polynya and one of the most productive regionsin the Arctic. This area of thin to absent sea ice is a critical moisturesource for local ice sheet sustenance and, coupled with the inflow ofnutrient-rich Arctic Surface Water, supports a diverse community of Arcticfauna and indigenous people. Although paleoceanographic records provideimportant insight into the NOW's past behavior, it is critical that webetter understand the modern functionality of paleoceanographic proxies. Inthis study, we analyzed lipid biomarkers, including algal highly branchedisoprenoids and sterols for sea ice extent and pelagic productivity andarchaeal glycerol dibiphytanyl glycerol tetraethers (GDGTs) for ocean temperature, in a set of modern surface sedimentsamples from within and around the NOW. In conjunction with previouslypublished datasets, our results show that all highly branched isoprenoidsexhibit strong correlations with each other and not with sterols, whichsuggests a spring or autumn sea ice diatom source for all highly branched isoprenoids (HBIs) rather than acombination of sea ice and open-water diatoms as seen elsewhere in theArctic. Sterols are also highly concentrated in the NOW and exhibitstatistically higher concentrations here compared to sites south of the NOW,consistent with the order of magnitude higher primary productivity observedwithin the NOW relative to surrounding waters in spring and summer months.Finally, our local temperature calibrations for GDGTs and OH-GDGTs reducethe uncertainty present in global temperature calibrations but alsoidentify some additional variables that may be important in controllingtheir local distribution, such as nitrate availability and dissolved oxygen.Collectively, our analyses provide new insight into the utility of theselipid biomarker proxies in high-latitude settings and will help provide arefined perspective on the past development of the NOW with theirapplication in downcore reconstructions. 

Abstract. Marine fronts delineate the boundary between distinct water masses and,through the advection of nutrients, are important facilitators of regionalproductivity and biodiversity. As the modern climate continues to change, themigration of frontal zones is evident, but a lack of information about theirstatus prior to instrumental records hinders future projections. Here, wecombine data from lipid biomarkers (archaeal isoprenoid glycerol dibiphytanylglycerol tetraethers and algal highly branched isoprenoids) with planktic andbenthic foraminifera assemblages to detail the biological response of themarine Arctic and polar front migrations on the North Iceland Shelf (NIS) overthe last 8 kyr. This multi-proxy approach enables us to quantify thethermal structure relating to Arctic and polar front migration and test howthis influences the corresponding changes in local pelagic productivity. Ourdata show that following an interval of Atlantic water influence, the Arcticfront and its associated high pelagic productivity migrated southeastward tothe NIS by ∼6.1 ka. Following a subsequent trend in regionalcooling, Polar Water from the East Greenland Current and the associated polarfront spread onto the NIS by ∼3.8 ka, greatly diminishinglocal algal productivity through the Little Ice Age. Within the last century,the Arctic and polar fronts have moved northward back to their currentpositions relative to the NIS and helped stimulate the productivity thatpartially supports Iceland's economy. Our Holocene records from the NISprovide analogues for how the current frontal configuration and theproductivity that it supports may change as global temperatures continue torise. 

ABSTRACT 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. 

Abstract We investigate the amplitude and frequency of directional geomagnetic change since 15 ka in the Northern North Atlantic (∼67°N) using five “ultra‐high” resolution continental shelf sediment cores deposited at rates greater than 1 m/kyr. The ages of these cores are constrained by 103 radiocarbon dates with reservoir ages assessed through tephra correlation to terrestrial archives. Our study aims to address many of the uncertainties that are common in sedimentary paleomagnetic studies, including signal attenuation in low to moderate resolution archives and difficulty to demonstrate reproducibility in higher resolution archives. The “ultra‐high” accumulation rates of our cores reduce “lock‐in” and smoothing uncertainties associated with magnetic acquisition processes. Abundant radiocarbon dates along with an objective alignment algorithm provide a test of signal reproducibility at sub‐millennial timescales. The paleomagnetic secular variation (PSV) signal, evaluated as individual records and as a new stack (GREENICE15k), validates prior results, but provides stronger geochronological constraints, demonstrates a reproducible PSV signal and amplitude, and extends through the abrupt Bølling–Allerød and Younger Dryas climate transitions of the latest Pleistocene. While broadly consistent with time‐varying spherical harmonic models and varve dated records from Northern Europe, we demonstrate greater variance and higher amplitudes—particularly at sub‐millennial timescales. This robust variability on centennial timescales is rarely observed or discussed, but is likely important to our understanding of some of the most intriguing aspects of the geodynamo.