WP5: Observations of the Arctic Ocean water column and sea ice cover

The main tasks are:



WP5.1: Multipurpose low frequency acoustic network

Work package leaders: Hanne Sagen (NERSC), Stein Sandven (NERSC)
Contributions from: Mathilde Sørensen (UiB)

Introduction

The Arctic ice-covered ocean is among the least observed and investigated oceans in the world. Physical and biological processes in the water column under the sea ice are poorly understood. The ongoing climate change in the Arctic is well documented, but there are many open questions about the role of the Arctic Ocean in the climate system. GoNorth can provide logistics and technology to install and operate observing systems for the deep Arctic Ocean.

Regional acoustic networks for acoustic thermometry, underwater GPS, and passive acoustics have been developed and implemented over the last ten years in several ocean areas, including the marginal ice zones of the Arctic (e.g. Mikhalevsky et al. 2015; Sagen et al. 2016). In these regional systems acoustic sources transmitting sweeps from 200 Hz to 300 Hz have been used in integration with advanced tomographic receiver arrays (e.g. Morozow et al. 2016). This system has been gradually tailored for and built up in the Fram Strait through the projects FP7 DAMOCLES, FP7 & RCN ACOBAR, and NFR UNDER-ICE (Sandven et al. 2014; Mikhalevsky et al 2015; Sagen et al. 2017). Inversion procedure for producing acoustically derived mean ocean temperature (accuracy 50 mC) is established for the Fram Strait (Sagen et al. 2016). Fig. 5.1.1. shows a time series of range-depth mean ocean temperature resulting from inversion acoustic travel-times between a source and receiver pair in the Fram Strait. Extended systems was deployed in 2010-2012 covering three tracks (Sagen et al. 2017) and seven tracks in 2014-2016 (UNDER-ICE project).

A similar acoustic monitoring system was deployed summer 2016 in the Beaufort Sea by the Scripps Institution of Oceanography (SIO) using the same technology. Furthermore, Canadian research groups aim to build up a similar system in the Baffin Bay (Eric Rehm, University of Laval, Canada).

Main objectives

GoNorth will prepare and deploy a pilot for a year-round multi-disciplinary observing system to collect oceanographic data including ocean temperature (mean temperature and point measurements), acidification, sea level, sea ice thickness, vocalizing marine life, acoustic impact of human activities, and geophysical hazardous events (e.g. earthquakes, landslides, tsunamis.



WP5.2: Physical oceanography and sea ice

Work package leaders: Stein Sandven (NERSC), Hanne Sagen (NERSC)

Introduction

During the last decades the Arctic Ocean has been strongly impacted by global warming. The atmospheric surface air temperature has increased twice as much compared with the global temperature, and the ice cover area and volume has decreased dramatically during summer time. Furthermore, the projection of summer ice indicates that the summer ice will potentially disappear under a doubling of CO2, perhaps by the middle of this century. This will have strong impact on the air-ocean interactions and the global climate.

The Arctic Ocean is characterized by three major current systems: 1) The inflow of warm Atlantic water north of Svalbard with core temperature of 3 to 5 °C; 2) The Transpolar Current across the Arctic Ocean being the most pronounced current in the Arctic Ocean. This current interacts with 3) The Beaufort Gyre, but the variability of and interactions between these current systems are not very well known. Furthermore, the deeper circulation in the Gakkel Ridge region is unknown. All these current systems, including the future development of the ice cover, need to be investigated in order to reveal the evolution of the climate of the Arctic Ocean. Model simulations indicate that the Transpolar Current may even disappear under a future global warming scenario.

The extent and types of sea ice are well observed by satellite systems, but sea ice thickness distribution in both space and time is much less known (Fig. 5.2.1). Knowledge about ice thickness is fundamental for calculating the volume and mass of the Arctic sea ice and for heat flux from ocean to atmosphere. Sea ice thickness data from satellites have large uncertainties, and therefore in situ observations both for the under- and top side of the ice are required jointly with heat flux measurements.

Main objective

Investigate the variability and interactions between the inflow of warm water north of Svalbard, the Transpolar Gyre and the Beafort Gyre.



WP5.3: Water column biology

Work package leaders: Jørgen Berge (UiT) and Malin Daase (UiT)

Introduction

The complex interactions among the biosphere, hydrosphere and cryosphere are central, yet poorly understood, features of the Arctic Ocean. A perturbation in one or more may propagate and amplify through complex interactions, resulting in disproportionally large changes and/or regime shifts. Disproportionally fast warming of the Arctic and loss of sea ice are well-known examples of such amplifications that will eventually result in a seasonally open, highly illuminated, and freshened Arctic Ocean. An ice-free Arctic summer is likely to occur within the next few decades (Stroeve et al. 2014), posing significant challenges for ice-obligate flora and fauna. Recent work summarized over 1000 species from Arctic sea-ice communities (Poulin et al. 2011), most of them with unknown life cycles, physiology and ecosystem relevance, making predictions of their fate in an ice-free Arctic extremely challenging. Processes in the sea ice are also tightly coupled to those in the water column. Alterations in sea-ice cover affect the underwater light climate and this together with changes in stratification, freshwater input and nutrient availability will modify the timing, productivity and relative significance of algal growth in the ice and the water column (Leu et al. 2015). This in turn will affect pelagic secondary producers whose life cycles are sharply tuned to the bloom phenology, leading to altered pelagic trophic dynamics and shifts in phenology cascading through all pelagic trophic levels (Søreide et al. 2010). Furthermore, changes in sea ice, stratification, and upwelling will affect the biochemical carbon cycle (Tremblay et al., 2011), while increased inflow of Atlantic water, an increase in open water area and changes in phenology lead to species range expansions. Thus as seasonal ice–free Arctic Ocean is likely to have both direct and indirect impacts on marine organisms, their interactions and ultimately on ecosystem processes across the entire water column.

The Arctic Marine Ecosystem Research Network (ARCTOS network) was established in 2002 and combines the expertise of north Norwegian and international institutions to achieve an integrated view of Arctic ecosystems, both locally and with a view across the Arctic. The Arctic University of Norway (UiT), the Norwegian Polar Institute, the University Centre in Svalbard, Akvaplan-Niva, the Institute of Marine Research and Nord University comprise the six basic ARCTOS institutions. Research conducted by ARCTOS members includes biological, physical, and chemical drivers that combined provide a holistic approach to marine ecosystems and across the food chain. State-of-the-art research tools, modelling platforms scaled to a variety of levels and processes, and modern infrastructure provide a strong foundation for basic research and student training.

Main objectives

To gain a better understanding how physical, biological and biochemical drivers regulated by the presence of sea ice influence the ecological processes in the water column below.