The holoceNe hisTory of Nares sTraiT Transition from glacial Bay to arctic-atlantic Throughflow

narrowest aBsTracT. Retreat of glacier ice from Nares Strait and other straits in the Canadian Arctic Archipelago after the end of the last Ice Age initiated an important connection between the Arctic and the North Atlantic Oceans, allowing development of modern ocean circulation in Baffin Bay and the Labrador Sea. As low salinity, nutrient-rich, Arctic Water began to enter Baffin Bay, it contributed to the Baffin and Labrador currents flowing southward. This enhanced freshwater inflow must have influenced the sea ice regime and likely is responsible for poor calcium carbonate preservation that characterizes the Baffin Island margin today. Sedimentologic and paleoceanographic data from radiocarbon-dated core HLY03-05GC, Hall Basin, northern Nares Strait, document the timing and paleoenvironments surrounding the retreat of waning ice sheets from the Nares Strait and opening of this connection between the Arctic Ocean and Baffin Bay. Hall Basin was deglaciated soon before 10,300 cal yrs BP (calibrated years before present) and records ice-distal sedimentation in a glacial bay facing the Arctic Ocean until about 9,000 cal yrs BP. Atlantic Water was present in Hall Basin during deglaciation, suggesting that it may have promoted ice retreat. A transitional unit with high ice-rafted debris content records the opening of Nares Strait at approximately 9,000 cal yrs BP. High productivity in Hall Basin between 9,000 and 6,000 cal yrs BP reflects reduced sea ice cover and duration as well as throughflow of nutrient-rich Pacific Water. The later Holocene is poorly resolved in the core, but slow sedimentation rates and heavier carbon isotope values support an interpretation of increased sea ice cover and decreased productivity during the Neoglacial period. surface o the bioturbated

There is strong geological evidence that Nares Strait was obstructed during the last glaciation by the coalescent Greenland and Innuitian Ice Sheets and was not deglaciated until the early Holocene (Blake, 1970;Zreda et al., 1999;England, 1999) Division (Falkner, 2003).  (Parnell et al., 2007;Funder, 1989). This 530 km long channel is 40 km wide at its narrowest aBsTr acT. Retreat of glacier ice from Nares Strait and other straits in the Canadian Arctic Archipelago after the end of the last Ice Age initiated an important connection between the Arctic and the North Atlantic Oceans, allowing development of modern ocean circulation in Baffin Bay and the Labrador Sea. As low salinity, nutrient-rich, Arctic Water began to enter Baffin Bay, it contributed to the Baffin and Labrador currents flowing southward. This enhanced freshwater inflow must have influenced the sea ice regime and likely is responsible for poor calcium carbonate preservation that characterizes the Baffin Island margin today. Sedimentologic and paleoceanographic data from radiocarbon-dated core HLY03-05GC, Hall Basin, northern Nares Strait, document the timing and paleoenvironments surrounding the retreat of waning ice sheets from the Nares Strait and opening of this connection between the Arctic Ocean and Baffin Bay. Hall Basin was deglaciated soon before 10,300 cal yrs BP (calibrated years before present) and records ice-distal sedimentation in a glacial bay facing the Arctic Ocean until about 9,000 cal yrs BP.
Atlantic Water was present in Hall Basin during deglaciation, suggesting that it may have promoted ice retreat. A transitional unit with high ice-rafted debris content records the opening of Nares Strait at approximately 9,000 cal yrs BP. High productivity in Hall Basin between 9,000 and 6,000 cal yrs BP reflects reduced sea ice cover and duration as well as throughflow of nutrient-rich Pacific Water. The later Holocene is poorly resolved in the core, but slow sedimentation rates and heavier carbon isotope values support an interpretation of increased sea ice cover and decreased productivity during the Neoglacial period.  (Aagaard and Carmack, 1989;Goose et al., 2007;Munchow et al., 2006). The freshwater and sea ice export through CAA straits is estimated to be responsible for only about 30% of total Arctic Ocean export, but modeling studies show that it can have a major impact on point, and 220 m deep at its shallowest sill in Kane Basin (Tang et al., 2004;Münchow et al., 2006). Nares Strait is at least 80% covered by sea ice for 11 months of the year.
Multiyear ice in the Arctic Ocean converges in the Lincoln Sea in mid to late winter, forming an ice arch that completely blocks the flow of Arctic Ocean ice through Nares Strait (Kwok, 2005). Locally formed pack ice consolidates south of the ice arch and remains into the late summer, with the transition from landfast to drift ice usually occurring between mid-July and mid-August (Melling et al., 2001). Ice arches form at other constrictions along the strait including Robeson Channel, Kennedy Channel, and Smith Sound (Samelson et al., 2006). They impede sea ice transit through the strait and promote the formation of the North Open Water polynya in northern Baffin Bay (Melling et al., 2001). The ice breaks out from south to north along Nares Strait. Sea ice can move at rates as high as 40 km per day (Kwok, 2005), driven by strong orographic and katabatic winds (Samelson et al., 2006 r r r r r r r r r r r r r r r r r r r r r r r re e e e e e e e e e e e e e e e e e e e e e e e Ellesmere I I I I I I I I I I I Isla sla l l l sla sla sla sla sla sla sla sla sla a d nd nd nd nd nd nd nd nd nd nd nd nd nd nd I I I I I I Isla l sla sla sla sla sla sla a d nd nd nd nd nd nd nd nd d I I I l l l l l l d d d d d d I I I l l l d d d Island figure 1. (a) surface circulation in the arctic ocean showing summer sea ice (light blue), the pathway of arctic surface water, made up largely of nutrient-rich, relatively low-salinity pacific water entering from Barrow strait through Nares strait, and of atlantic water entering the arctic ocean via fram strait and the Barents sea. The atlantic water flows as a subsurface "atlantic layer" in the arctic ocean, entering Nares strait beneath the arctic water. (b) map showing details of Nares strait physiography, the location of hly03-05gc, the box that encloses figure 6, the 450 m deep sill at the mouth of petermann glacier fjord, and the location of core lssl2001-079. rc = robeson channel. hB = hall Basin. Kc = Kennedy channel. flows southward from the Arctic Ocean through Nares Strait into Baffin Bay driven by winds and the sea level drop along the length of the strait (Sadler, 1976;Münchow et al., 2006). The upper 100 m of the water column in Nares Strait is made up of low-salinity Arctic Water composed largely of nutrient-rich Pacific Water that enters the Arctic Ocean via the Bering Strait, as well as freshwater from river runoff and sea ice melt (Münchow et al., 2007). Pacific water has twice the nitrogen and phosphorus, and seven times the silica, of Atlantic Water, which fuels the high phytoplankton productivity of the Arctic shelves in surface water when sea ice cover retreats, thereby fueling benthic production.
Along most of the length of Nares Strait, relative sea level was 80 to 120 m higher " reTreaT of glacier ice from Nares sTraiT aNd oTher sTraiTs iN The caNadiaN arcTic archipelago afTer The eNd of The lasT ice age iNiTiaTed aN imporTaNT coNNecTioN BeTweeN The arcTic aNd The NorTh aTlaNTic oceaNs, allowiNg deVelopmeNT of moderN oceaN circulaTioN iN BaffiN Bay aNd The laBrador sea. " than present in the early Holocene in response to retreat of the ice sheet and unloading of the crust (Funder and Hansen, 1996;England et al., 2006). As a result, water depths along Nares Strait and at the entrance to the Arctic Ocean were considerably deeper in the early Holocene than they are today.
One other marine sediment core has been taken in the area. LSSL2001-079 PC consists of 8 m of calcareous mud ( Figure 1). Radiocarbon dates in this core formed age reversals, and a radiocarbon date of 14,070 ± 100 14 C yrs BP in stratified sediments was interpreted to indicate that Hall Basin had not been inundated by grounded ice for at least 16,800 cal years (Mudie et al. 2006). It is unclear what material was dated and whether there was a source of old carbon to produce this date. In any event, the interpretation of the "old" date in LSSL2001-079PC conflicts with the glacial history presented from terrestrial glacial records (England, 1999;Kelly and Bennike, 1992) and data presented in this paper.

maTerials aNd meThods
The site for collection of HLY03-05GC was chosen on the basis of acoustic profiles and swath bathymetry.  (Table 1). We present calibrated ages and 14 C ages using a 400-year ocean reservoir correction (i.e., DR=0) for all samples and boundaries within the core in order to make the clearest comparison with the published glacial history concerning the Innuitian Ice Sheet, which is reported in 14 C years corrected for an ocean reservoir age of 400 or 410 years (R = 400 or 410 yrs). We recognize that a larger ocean reservoir correction likely is needed for some of the 14 C dates on marine carbonates from the Canadian Arctic Archipelago. A large ocean reservoir age of 735 ± 85 yrs has been carefully determined (Dyke et al., 2003;Coulthard et al., 2010), so  (Funder et al., in press;Möller et al., 2010;Larsen et al., 2010). We calibrated the radiocarbon dates from HLY03-05GC using Calib 6.0 (Stuiver et al., 2010) with the Marine09 calibration curve (Reimer et al., 2009; Table 1).
The HLY03-05GC record extends from 160 to 10,300 cal yrs BP (130-9,010 14 C yrs BP). The age model for the core is a 0-weight curve fit between the dated levels ( Figure 2). Basin as the origin for the laminated unit (Pickering et al., 1986;Ó Cofaigh and Dowdeswell, 2001), which is consistent with distal glacial marine sedimentation (Syvitski and Hein, 1991 (Parnell et al., 2007).
In support of the Atlantic Water hypothesis, the HLY03-05GC data suggest that the Atlantic Layer was present in Hall Basin throughout the period of deglaciation, and it likely assisted rapid melting of the marine based ice outlet (cf. Holland et al., 2008).
An inconsistency arises between the terrestrial-based reconstruction (England, 1999) (England, 1999). However, the presence of distal glaciomarine sediments in HLY03-05 GC with a 14 C date on foraminifers of 8,920 14 C yrs BP  England (1999) and England et al. (2006), the strait was still closed at 8,000 14 C yrs BP, but the opening was established by 7,500 14 C yrs BP. Considering the vastly different data sets, this age comparison is quite close. changes in sea ice cover and marine productivity: holocene climatic optimum to Neoglacial cooling  (Funder and Weidick, 1991), and dinoflagellate and foraminiferal data also indicate early Holocene warmth (Levac et al., 2001;Knudsen et al., 2008). On northern Greenland, an area that today has heavy multiyear sea ice cover and landfast ice, wave-generated beach ridge complexes dated to between 8,500 and Ocean with Baffin Bay, shows consistent sea ice history, with an early Holocene interval of low spring sea ice occurrence between 10,000 and 6,000 cal yrs BP and a moderate increase in spring sea ice between 6,000 and 4,000 cal yrs BP (Vare et al., 2009).
There is strong evidence in the region for Neoglacial cooling beginning between 6,000 and 5,500 cal yrs BP (England et al., 2008;Möller et al., 2010;Funder et al., 2009;Polyak et al., 2010;Vare et al., 2009). Unfortunately, the HLY03-05 GC record is not well resolved in this interval because the sedimentation rates are very slow, and the sampling interval was too wide to capture the late Holocene record. However, we surmise that the very slow sedimentation rates and decreases in productivity-indicator benthic foraminifers are consistent with increased sea ice cover and reduced marine productivity in the late Holocene in Hall Basin (Figure 7). The Neoglacial period is consistently associated with cooling and increased duration and thickness of sea ice cover on northern Greenland and in CAA. On northern Greenland, seasonally open water from 5,500 to 3,000 cal yrs BP allowed driftwood to land after rafting on sea ice, but from 3,000 to 1,000 cal yrs BP, there is very little driftwood indicating more severe sea ice conditions with landfast or multiyear sea ice (Funder et al., 2009).
On northern Ellesmere Island, the driftwood record ceases at 5,500 cal yrs BP, documenting the onset of multiyear landfast sea ice and formation of the sea ice shelves, most notably the Ward Hunt Ice Shelf (England et al., 2008). A sharp increase in spring sea ice occurrence was reconstructed beginning by 3,000 cal yrs BP on the basis of IP25 data and biological proxies in several widely spaced sediment cores from CAA (Vare et al., 2009;Belt et al., 2010;Knudsen et al., 2008;Levac et al., 2001).  . Key paleoceanographic proxies shown against calibrated age in hly03-05gc. occurrence of δ 18 o Nps in the laminated mud supports glacial meltwater entering the hall Basin from the retreating ice sheets. The holocene optimum is recorded by evidence of high marine productivity (N. iridea % and light δ 13 c C. neoteretis) and warming in the near surface layer (δ 18 o Nps). low sedimentation rates in the upper bioturbated mud precluded high-resolution evaluation of Neoglacial cooling, but the evidence shown is consistent with cooling after 6,000 cal yrs Bp.