Simon Prinsenberg

Monitoring the volume, freshwater and heat fluxes passing through Lancaster sound in the Canadian arctic archipelago

Abstract A research project, consisting of instrumentation development and mooring work, has monitored the volume, heat and freshwater fluxes passing through Lancaster Sound, one of the three main pathways through the Canadian Arctic Archipelago. Instrumentation to measure the current direction of the Acoustic Doppler Current Profilers (ADCPs) moored in this region of low horizontal magnetic field strength have been successfully developed and implemented. Time series data from August 1998 to September 2001 of the salinity, temperature and velocity fields and the derived estimates of the volume, freshwater and heat fluxes passing through Lancaster Sound are reported. The fluxes exhibit large seasonal and interannual variabilities. Fluxes are small in fall and winter and reach their maxima in late summer. The seasonal eastward volume flux estimate ranged from a low of ‐0.01 Sv in the fall of 1998 to a maximum of 1.3 Sv in the summer of 2000. Its three‐year mean of 0.75 Sv varies interannually by ±0.25 Sv. Freshwater flux estimates vary similarly with minima in winter and maxima in late summer. They generally are one‐fifteenth of the volume fluxes; but are likely underestimated as their surface freshwater content is based on data from Conductivity‐Temperature‐Depth (CTD) sensors at 25–30 m depth thus missing fresher water above the summer halocline. The pack ice contribution to the freshwater flux is small as most of the year the pack ice is land‐fast; it accounts for less than 5% of the freshwater flux when spread over the entire year.

Perennial pack ice in the southern Beaufort Sea was not as it appeared in the summer of 2009

[1] In September 2009 we observed a much different sea icescape in the Southern Beaufort Sea than anticipated, based on remotely sensed products. Radarsat derived ice charts predicted 7 to 9 tenths multi-year (MY) or thick first-year (FY) sea ice throughout most of the Southern Beaufort Sea in the deep water of the Canada Basin. In situ observations found heavily decayed, very small remnant MY and FY floes interspersed with new ice between floes, in melt ponds, thaw holes and growing over negative freeboard older ice. This icescape contained approximately 25% open water, predominantly distributed in between floes or in thaw holes connected to the ocean below. Although this rotten ice regime was quite different that the expected MY regime in terms of ice volume and strength, their near-surface physical properties were found to be sufficiently alike that their radiometric and scattering characteristics were almost identical.

Observations in the Ocean

The chapter begins with an overview of the exploratory work done in the Arctic Ocean from the mid nineteenth century to 1980, when its main features became known and a systematic study of the Arctic Ocean evolved. The following section concentrates on the decade between 1980 and 1990, when the first scientific icebreaker expeditions penetrated into the Arctic Ocean, when large international programme were launched, and the understanding of the circulation and of the processes active in the Arctic Ocean deepened. The main third section deals with the studies and the advances made during the ACSYS decade. The section has three headings: the circulation and the transformation of water masses; the changes that have been observed in the Arctic Ocean, especially during the last decades; and the transports between the Arctic Ocean and the surrounding world ocean through the different passages, Fram Strait, Barents Sea, Bering Strait and the Canadian Arctic Archipelago. In section four, the Arctic Ocean is considered as a part of the Arctic Mediterranean Sea, and the impacts of possible climatic changes on the circulation in the Arctic Mediterranean and on the exchanges with the world ocean are discussed.

Observing and interpreting the seasonal variability of the oceanographic fluxes passing through Lancaster Sound of the Canadian Arctic Archipelago

As part of the Arctic/Sub-Arctic Ocean Flux (ASOF) and the International Polar Year (IPY) programs, a research project consisting of mooring and analysis work has studied the ocean and ice fluxes passing through Lancaster Sound, one of the three main pathways through the Canadian Arctic Archipelago (CAA) since 1998. The aim is to understand the variability in ocean and sea ice volume, heat and freshwater fluxes passing through the CAA and to determine their relationship to the ocean and ice budgets of the Arctic Ocean itself and to the circulation and vertical ventilation of the North Atlantic Ocean. Eight years of mooring data have now been processed and analyzed. The volume, freshwater and heat fluxes exhibit large seasonal and interannual variabilities with small fluxes in the fall and early winter and large fluxes in the summer. The seasonal mean volume flux estimates range from a low of 0.0Sv in the fall of 1998 to a maximum of 1.3Sv in the summer of 2000 (1Sverdrup=1.0x10ms). It has an 8yr annual mean of 0.7Sv and varies interannually by ±0.3Sv. Model simulations indicate that fluxes through Lancaster Sound make up 40-50% of the fluxes through the entire Canadian Arctic Archipelago, and that they are dependent on the sea level difference between the Beaufort Sea and Baffin Bay and on the horizontal density gradients across the CAA, observations of which are scarce or non-existent. Regression analysis with the Arctic Ocean wind field shows that the fluxes through the NW Passage measured in Lancaster Sound are significantly correlated with the far field wind forcing in the Beaufort Sea. The northeastward winds in the Beaufort Sea, parallel to the western side of the Canadian Arctic Archipelago, show the highest correlation on monthly to interannual time scales. This result is consistent with the transport being driven by a sea level difference between opposite ends of the NW Passage, and the difference being determined by setup caused by alongshore winds in the Beaufort Sea.

Observations of sea ice thickness, surface roughness and ice motion in Amundsen Gulf

[1] Ice thickness and surface roughness measurements of first-year (FY) sea ice were collected with a fix-mounted helicopter-borne electromagnetic (HEM) -laser system in Amundsen Gulf in April to May 2004. The modal ice thickness values are in good qualitative agreement with different ice types identified in synthetic aperture radar (SAR) imagery and shown on ice charts produced by the Canadian Ice Service. Modal ice thickness values which generally represent level ice thicknesses were about 2.0 m over landfast ice. A large range of modal ice thicknesses was observed in the mobile ice region, with values of about 0.2 m (young ice) in leads (where there was high radar backscatter), 0.6 m (thin FY ice) in the polynya (where there was medium to high backscatter), and about 1.1-1.9 m (thick FY ice) elsewhere. High surface roughnesses are strongly associated with high radar backscatter in SAR imagery, and are observed in areas of large shear. The ratio of the standard deviations of ice draft and averaged roughness in an area of landfast ice is in good agreement with the ratio of the standard deviations of ice draft and ice-equivalent roughness expected from isostasy, with constant level ice and snow thickness. However, the standard deviation of ice-equivalent roughness may be significantly underestimated, due to differences in snow thickness between level and deformed ice, and limitations of the laser processing method. Modal ice (plus snow) thicknesses measured with the HEM system are within the range of historical values measured at Cape Parry.

Implications of fractured Arctic perennial ice cover on thermodynamic and dynamic sea ice processes

Decline of the Arctic summer minimum sea ice extent is characterized by large expanses of open water in the Siberian, Laptev, Chukchi, and Beaufort Seas, and introduces large fetch distances in the Arctic Ocean. Long waves can propagate deep into the pack ice, thereby causing flexural swell and failure of the sea ice. This process shifts the floe size diameter distribution smaller, increases floe surface area, and thereby affects sea ice dynamic and thermodynamic processes. The results of Radarsat-2 imagery analysis show that a flexural fracture event which occurred in the Beaufort Sea region on 6 September 2009 affected ∼40,000 km2. Open water fractional area in the area affected initially decreased from 3.7% to 2.7%, but later increased to ∼20% following wind-forced divergence of the ice pack. Energy available for lateral melting was assessed by estimating the change in energy entrainment from longwave and shortwave radiation in the mixed-layer of the ocean following flexural fracture. 11.54 MJ m−2 of additional energy for lateral melting of ice floes was identified in affected areas. The impact of this process in future Arctic sea ice melt seasons was assessed using estimations of earlier occurrences of fracture during the melt season, and is discussed in context with ocean heat fluxes, atmospheric mixing of the ocean mixed layer, and declining sea ice cover. We conclude that this process is an important positive feedback to Arctic sea ice loss, and timing of initiation is critical in how it affects sea ice thermodynamic and dynamic processes.

Change and variability in sea ice during the 2007–2008 Canadian International Polar Year program

In this paper we describe sea ice change and variability during the Canadian International Polar Year (IPY) program and examine several regional and hemispheric causes of this change. In a companion paper (Barber et al., Climate Change2012) we present an overview of the consequences of this observed change and variability on ecosystem function, climatically relevant gas exchange, habitats of primary and apex predators, and impacts on northern peoples. Sea ice-themed research projects within the fourth IPY were designed to be among the most diverse international science programs. They greatly enhanced the exchange of Inuit knowledge and scientific ideas across nations and disciplines. This interdisciplinary and cultural exchange helped to explain and communicate the impacts of a transition of the Arctic Ocean and ecosystem to a seasonally ice-free state, the commensurate replacement of perennial with annual sea ice types and the causes and consequences of this globally significant metamorphosis. This paper presents a synthesis of scientific sea ice research and traditional knowledge results from Canadian-led IPY projects between 2007 and 2009. In particular, a summary of sea ice trends, basin-wide and regional, is presented in conjunction with Inuit knowledge of sea ice, gathered from communities in northern Canada. We focus on the recent observed changes in sea ice and discuss some of the causes of this change including atmospheric and oceanic forcing of both dynamic and thermodynamic forcing on the ice. Pertinent results include: 1) In the Amundsen Gulf, at the western end of the Northwest Passage, open water persists longer than normal and winter sea ice is thinner and more mobile. 2) Large areas of summer sea ice are becoming heavily decayed during summer and can be broken up by long-period waves being generated in the now extensive open water areas of the Chukchi Sea. 3) Cyclones play an important role in flaw leads—regions of open water between pack ice and land-fast ice. They delay the formation of new ice and the growth of multi-year ice. 4) Feedbacks involving the increased period of open water, long-period wave generation, increased open-ocean roughness, and the precipitation of autumn snow are all partially responsible for the observed reduction in multiyear sea ice. 5) The atmosphere is observed as remaining generally stable throughout the winter, preventing vertical entrainment of moisture above the surface.

Observing regional-scale pack-ice decay processes with helicopter-borne sensors and moored upward-looking sonars

Abstract The variability of Arctic pack-ice parameters (e.g. extent and ice type) has been monitored by satellite-borne sensors since the early 1960s, and information on ice thickness is now becoming available from satellite altimeters. However, the spatial resolution of satellite-derived ice properties is too coarse to validate fine-scale ice variability generated by regional-scale interaction processes that affect the coarse-scale pack-ice albedo, strength and decay. To understand these regional processes, researchers rely on other data-monitoring platforms such as moored upward-looking sonars and helicopter-borne sensors. Backed by observations, two such regional-scale pack-ice decay processes are discussed: the break-up of large pack-ice floes by long-period waves generated by distant storms, and the spring decay of first-year-ice ridges in a diverging pack-ice environment. These two processes, although occurring on regional spatial scales, are important contributors to the evolution of the total pack ice and need to be included in global climate models, especially as the conditions for their occurrence will alter due to climate change.

Comparison of airborne electromagnetic ice thickness data with NOAA/AVHRR and ERS‐1/SAR images

Abstract Snow‐plus‐ice thickness and surface‐ice roughness data collected by a helicopter‐towed sensor package was used to identify surface‐ice properties in March 1992 AVHRR and SAR images for the land‐fast and mobile pack ice off the northern coast of Newfoundland. The sensor package consisted of an electromagnetic induction sensor and laser profilometer. Observed snow depths and ice thicknesses verified that snow‐plus‐ice thickness over undeformed ice can be obtained to an accuracy of ±10 cm. Snow‐plus‐ice thickness and surface roughness data for flight sections covering several hundred kilometres indicated the change in pack ice properties seen in images from thin, smooth coastal ice and open water conditions to thick, rough consolidated offshore pack ice. Ice charts covering the same area showed similar variations in ice conditions based on AVHRR and fixed‐wing reconnaissance data. In the ERS‐1 SAR image, low backscattering coefficients were associated with large, smooth coastal floes interspersed wi...

Model simulated volume fluxes through the Canadian Arctic Archipelago and Davis Strait: Linking monthly variations to forcing in different seasons

The solution of a 10 year simulation of the Arctic Ocean, produced using a 6 km resolution coupled ocean and sea-ice model, is analyzed to understand the variability, control, and forcing mechanisms of the volume fluxes through the Canadian Arctic Archipelago (CAA) and Davis Strait (DS). The analysis focuses on variability at monthly time scales. Analysis confirms the “control” of volume fluxes through the CAA, proposed in previous studies, by (1) variations of sea surface height (SSH) in the “upstream” regions and the relationship of this control to alongshore wind in the Beaufort Sea and (2) by SSH in the “downstream” region in Baffin Bay that may be related to wind stress in Baffin Bay and the northern Labrador Sea. The effectiveness of these control and forcing mechanisms vary for fluxes through different sections and for different seasons. Variation of the southward flux through DS is directly influenced by fluxes through Nares Strait (NS) and Barrow Strait (BS) in summer, fall, and winter. In spring, variations of the southward and northward fluxes through DS are closely related to each other and correspond to changes in the SSH along pathways of the Irminger Current, and the East and West Greenland Currents.