Science Background

Freshwater and Heat: The Arctic freshwater cycle is a longstanding framework for efforts to quantify and understand Arctic change due to its important role in modulating the Arctic energy balance and, further afield, global climate (e.g. Prowse et al., 2015; Carmack et al., 2016). Freshwater enters the Arctic upper ocean primarily through river discharge, Bering Strait inflow and net precipitation, with the majority exiting about equally though the Canadian Arctic Archipelago (CAA) and Fram Strait (Serreze et al., 2006; Haine et al., 2015). Because salinity controls Arctic Ocean stratification, this freshwater creates a cold, buoyant layer below the ice-ocean interface that insulates the surface from the warmer, more saline Atlantic waters below, thus modulating sea ice formation and melt and, through this, coupling between the upper ocean and local atmospheric forcing. Freshwater and heat exchange between the Arctic and North Atlantic provide critical mechanisms through which the Arctic and global climate interact. Arctic freshwater discharges through Davis and Fram straits near deepwater formation regions west and east of Greenland, where its buoyancy may act to modulate convective overturning and deepwater formation (e.g., Karcher et al., 2005; Jahn and Holland, 2013, Yang et al., 2016). Changes in Arctic freshwater outflow also modulate the extent and strength of the North Atlantic subpolar gyre, which can have profound impacts on fisheries (Hátún et al., 2009), nutrient flux (Hátún et al., 2017) and on carbon uptake and storage (Schuster and Watson, 2007) in this highly productive region. Additionally, northward penetration of warm Atlantic waters along the Greenland coast may accelerate the melting of marine terminating glaciers (e.g., Holland et al., 2008, Straneo and Heimbach, 2013, Myers and Ribergaard 2013, Gladish et al., 2014), injecting additional freshwater into the system and contributing to sea level rise.

General circulation in Baffin Bay and Davis Strait (white arrows) and the location of the 2004–10 moored array (red line). AW, by way of the CAA, leaves Davis Strait as the broad, surface-intensified BIC. Northward flow on the eastern side of Davis Strait consists of the fresh WGC of Arctic origin on the shelf and warm, salty WGSC of North Atlantic origin on the slope Curry et al., 2014.

Arctic Gateway: Davis Strait provides a single site for quantifying both CAA outflow and northward fluxes along the West Greenland slope and shelf that may impact land ice melt. The CAA component of Arctic outflow enters Baffin Bay though four distinct passages (Bellot Strait, Barrow Strait, Hell Gate/Cardigan Strait, and Nares Strait), undergoing numerous transformations along its transit to Davis Strait. By the time they reach Davis Strait, Arctic waters already embody most of the transformation they undergo prior to exerting their influence on the deepwater formation sites in the Labrador Sea. This makes the Strait an ideal site to quantify the variability and structure of the integrated CAA freshwater flux after it has undergone these complex transformations, and just prior to entering the Labrador Sea. Sustained observations at Davis Strait also provide early detection of corrosive Arctic outflow into the subpolar North Atlantic, where it may impact highly productive regions and important commercial fisheries and document changes in these chemical states and the marine ecosystem response to ocean acidification (Azetsu-Scott et al., 2010; Hammill et al., 2018).

The Davis Strait observing system. Black dots mark mooring sites, red dots mark hydirgraphic sampling stations and red tiangles indicate the poistions of bottom pressure sensors (2020 and beyond).

Project Overview

The Davis Strait observing system was established in 2004 to advance understanding of the role of Arctic – sub-Arctic interactions in the climate system by collecting sustained measurements of physical, chemical and biological variability at one of the primary gateways that connect the Arctic and subpolar oceans. Efforts began as a collaboration between researchers at the University of Washington’s Applied Physics Laboratory and the Canadian Department of Fisheries and Ocean’s Bedford Institute of Oceanography, but has grown to include researchers from the Greenland Institute of Natural Resources, Greenland Climate Institute, Danish Technological University, University of Alberta and University of Colorado, Boulder. The project is a component of the NSF Arctic Observing and Atlantic Meridional Overturning Networks, and the international Arctic-Subarctic Ocean Flux (ASOF) program, Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP), Global Ocean Acidification Observing Network (GOA-ON), Arctic Monitoring Assessment Programme (AMAP) and OceanSITES system.

(top) Davis Strait 2004–10 (red line) and 1987–90 (black line) moored arrays with squares indicating mooring locations. (bottom) Summary of Davis Strait 2004–10 moored array instrumentation. Blue crosses indicate SBE37 MicroCAT conductivity, temperature, and pressure recorders; green dots represent RDI ADCPs; black dots denote Aanderaa RCM8 velocity, conductivity, and temperature recorders; red dots denote Aanderaa RCM8 velocity and temperature recorders; and orange dots denote ULSs. Inset image shows a close-up of the Baffin Island shelf instruments. Spatial coverage varies from year to year throughout the program. Curry et al., 2014

The initial system employed a mooring array measuring temperature, salinity, velocity, ice draft and passive acoustics (for marine mammal presence), annual hydrographic sampling for chemical properties and year-round sampling using autonomous, long-endurance Seagliders. The program included development of new technologies to enable year-round measurements in ice-covered waters, specifically Seagliders with enhanced autonomy and acoustic navigation and an inexpensive, light-weight approach for collecting moored measurements near the ice-ocean interface. To decrease cost and thereby facilitate sustained operations, in recent years the measurement program has consolidated to rely solely on the mooring array and biennial chemical and bioloigical sampling, with the Seaglider component ending in 2014. Launched in 2020, the current system has expanded to include biological measurements across multiple trophic levels (phytoplankton to marine mammals) and numerical modeling at both regional and climate scales.

Highlights

Monthly volume and freshwater (relative to S = 34.8) between October 2004 and September 2012, calculated from objectively analyzed velocity and salinity fields, integrated from 640 m (sill depth) to the sea surface. Negative values indicate southward transport, with grey shading marking uncertainties in the estimates Curry et al., 2014.

Year-long sampling of Davis Strait by Seagliders. The background chart displays sea ice concentration from SMMR and SMM/I (National Snow and Ice Data Center and NASA Goddard Space Flight Center), with blue marking open water and white indicating full ice cover. Green symbols mark mooring locations. Gliders operating under ice cover geolocated using the array of acoustic navigation sources (moorings with green circles). Moving yellow, red and magenta symbols mark glider positions from three successive glider missions, with a 7-day tail. From 9 June 2010 - 17 Jun 2011, gliders occupied 34 repeat sections, with 7 months operating in partial or full ice cover.