THE CHANGING ARCTIC OCEAN | SpECIAL ISSUE ON THE IntERNATIONAL POLAR YEAr (2007–2009) THE HOLOCENE HISTORY OF NARES STRAIT Transition from Glacial Bay to Arctic-Atlantic Throughflow BY AnnE E. JEnnINGS, CHRISTINA SHELDON, THOMAS M. CRONIN, PIERRE FRANCUS, JOSEPH StONER, AND JOHN AnDREWS Moderate Resolution Imaging Spectroradiometer (MODIS) image from August 2002 shows the summer thaw around Ellesmere Island, Canada (west), and Northwest Greenland (east). As summer progresses, the snow retreats from the coastlines, exposing the bare, rocky ground, and seasonal sea ice melts in fjords and inlets. Between the two landmasses, Nares Strait joins the Arctic Ocean (north) to Baffin Bay (south). From http://visibleearth.nasa.gov/view_rec.php?id=3975 26 Oceanography | Vol.24, No.3 ABSTRACT. Retreat of glacier ice from Nares Strait and other straits in the Nares Strait and the subsequent evolu- Canadian Arctic Archipelago after the end of the last Ice Age initiated an important tion of Holocene environments. In connection between the Arctic and the North Atlantic Oceans, allowing development August 2003, the scientific party aboard of modern ocean circulation in Baffin Bay and the Labrador Sea. As low-salinity, USCGC Healy collected a sediment nutrient-rich Arctic Water began to enter Baffin Bay, it contributed to the Baffin and core, HLY03-05GC, from Hall Basin, Labrador currents flowing southward. This enhanced freshwater inflow must have northern Nares Strait, as part of a study influenced the sea ice regime and likely is responsible for poor calcium carbonate entitled “Variability and Forcing of preservation that characterizes the Baffin Island margin today. Sedimentologic and Fluxes Through Nares Strait and Jones paleoceanographic data from radiocarbon-dated core HLY03-05GC, Hall Basin, Sound: A Freshwater Emphasis” that was northern Nares Strait, document the timing and paleoenvironments surrounding sponsored by the US National Science the retreat of waning ice sheets from Nares Strait and opening of this connection Foundation, Office of Polar Programs, between the Arctic Ocean and Baffin Bay. Hall Basin was deglaciated soon before Arctic Division (Falkner, 2003). 10,300 cal BP (calibrated years before present) and records ice-distal sedimentation In this article, we investigate the in a glacial bay facing the Arctic Ocean until about 9,000 cal BP. Atlantic Water was timing of the opening of Nares Strait and present in Hall Basin during deglaciation, suggesting that it may have promoted the Holocene paleoceanographic devel- ice retreat. A transitional unit with high ice-rafted debris content records the opments during the deglaciation, the opening of Nares Strait at approximately 9,000 cal BP. High productivity in Hall Holocene Optimum, and the Neoglacial Basin between 9,000 and 6,000 cal BP reflects reduced sea ice cover and duration cooling that followed through multiproxy as well as throughflow of nutrient-rich Pacific Water. The later Holocene is poorly analysis of HLY03-05GC (81°37.286'N, resolved in the core, but slow sedimentation rates and heavier carbon isotope values 63°15.467'W, 372 cm long, 797 m water support an interpretation of increased sea ice cover and decreased productivity depth; Figure 1). The paleoenvironmental during the Neoglacial period. reconstruction uses lithofacies descrip- tions and analysis, radiocarbon dating, IntRODUCTION have a major impact on convection in benthic and planktic foraminiferal The Arctic Ocean influences the the Labrador Sea (Tang et al., 2004; assemblages, and oxygen and carbon global hydrological cycle by exporting Goosse et al., 2007). stable isotope analyses. Detailed analyses freshwater and sea ice to the North There is strong geological evidence on this single, well-placed sediment Atlantic Ocean through Fram Strait and that Nares Strait was obstructed during core complement the aerially extensive passages within the Canadian Arctic the last glaciation by the coalescent terrestrial-based studies of glacial and Archipelago (CAA), including Jones Greenland and Innuitian Ice Sheets sea ice history by providing a continuous, Sound, Lancaster Sound, and Nares and was not deglaciated until the early well-dated, Holocene marine record. Strait (Figure 1). Temporal and spatial Holocene (Blake, 1970; England, 1999; variations in freshwater fluxes stabilize Zreda et al., 1999). The deglaciation of Environmental Setting the water column and impede convective Nares Strait and the opening of a connec- Nares Strait separates Ellesmere Island overturning, thereby influencing global tion between the Arctic Ocean and Baffin from Greenland and stretches from thermohaline circulation (Aagaard and Bay must have been a significant factor northern Baffin Bay to the Lincoln Sea, Carmack, 1989; Münchow et al., 2006; in the paleoceanographic development Arctic Ocean (Figure 1). The bedrock Goose et al., 2007). The freshwater and and paleoclimate history of Baffin Bay geology of the ice-free areas along Nares sea ice export through CAA straits is and the Labrador Sea. However, because Strait is composed of Precambrian estimated to be responsible for only of its remote and ice-covered location, crystalline rocks overlain by Paleozoic about 30% of total Arctic Ocean export, few sediment cores have been collected platform carbonates (Funder, 1989; but modeling studies show that it can that might document the opening of Parnell et al., 2007). This 530 km long Oceanography | September 2011 27 180° 80°N 85°N Barrow St. a b 120° EllesmereEEllesmere IslandIsllandd Archer F Beaufort Smith Gyre Fig. 6 120° Sound d HLY03-01-05GC Kane Basin KC HB RC Lincoln Sea 85°N 75°N Transpolar LSSL2001-079 CAA Drift Petermann Gl Topography Nares Strait Ban 60° 5400 m Bay BC Fram 1 Greenland St. Bathymetry WGC Greenland 60° N. Atl. Current 0 EGC 70° N –2500 m 050 100 150 Kilometers 0 400 km 50°W 40°W 30°W 20°W 60° N 0° 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 A“ tlantic 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. Bathymetric base map from IBCAO (Jakobsson et al., 2008). channel is 40 km wide at its narrowest Sheet that terminates in a long, floating to late winter, forming an ice arch point, and 220 m deep at its shallowest ice shelf. Petermann Fjord is over that completely blocks the flow of sill in Kane Basin (Tang et al., 2004; 1,000 m deep near the glacier front, but Arctic Ocean ice through Nares Strait Münchow et al., 2006). From north this deep basin lies behind a 350–450 m (Kwok, 2005). Locally formed pack ice to south, Nares Strait is composed of deep sill at the fjord mouth that sepa- consolidates south of the ice arch and Robeson Channel, Hall Basin, Kennedy rates the fjord from the deep Hall Basin remains into the late summer, with Channel, Kane Basin, and Smith Sound (Figure 1b; Johnson et al., 2011). the transition from landfast to drift ice (Figure 1). Hall Basin is an 800 m deep Nares Strait is at least 80% covered usually occurring between mid-July and basin off Archer Fjord and Petermann by sea ice for 11 months of the year. mid-August (Melling et al., 2001). Ice Glacier Fjord, home of the Petermann Multiyear ice in the Arctic Ocean arches form at other constrictions along Glacier, an outlet of the Greenland Ice converges in the Lincoln Sea in mid the strait, including Robeson Channel, Kennedy Channel, and Smith Sound Anne E. Jennings ([email protected]) is Research Scientist III, Institute of Arctic (Samelson et al., 2006). They impede and Alpine Research (INSTAAR), and Associate Professor, Attendant Rank, Department sea ice transit through the strait and of Geological Sciences, University of Colorado, Boulder, CO, USA. Christina Sheldon is a promote the formation of the North graduate student, Department of Geological Sciences, University of Colorado, Boulder, Open Water polynya in northern Baffin CO, USA. Thomas M. Cronin is a research geologist, US Geological Survey, Reston, VA, Bay (Melling et al., 2001). The ice breaks USA. Pierre Francus is Professor, Institut national de la recherche scientifique (INRS), out from south to north along Nares Centre Eau Terre Environnement, Québec, Canada. Joseph Stoner is Associate Professor, Strait. Sea ice can move at rates as high College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA. as 40 km per day (Kwok, 2005), driven John Andrews is Professor Emeritus, INSTAAR, University of Colorado, Boulder, CO, USA. by strong orographic and katabatic 28 Oceanography | Vol.24, No.3 winds (Samelson et al., 2006). Water preservation of CaCO3 microfossils and confluent ice flowing from Nares Strait flows southward from the Arctic Ocean molluscs on its path along the Baffin into the Lincoln Sea (Funder et al., in through Nares Strait into Baffin Bay Island shelf southward along Labrador press). Heavy sea ice cover in the Arctic driven by winds and the sea level drop (Azetsu-Scott et al., 2010). Ocean is thought to have deflected along the length of the strait (Sadler, the shelf-based ice eastward along the 1976; Münchow et al., 2006). The upper Glacial History north coast of Greenland (Larsen et al., 100 m of the water column in Nares Strait Study of HLY03-05GC is framed by 2010). Minimal inflow of Atlantic Water is made up of low-salinity Arctic Water glacial geological reconstructions for beneath a thick halocline would have composed largely of nutrient-rich Pacific CAA (Blake, 1970; England, 1999; shielded the shelf-based ice (Larsen et al., Water that enters the Arctic Ocean via Dyke et al., 2002; England et al., 2006) 2010).