Searching for light in the Arctic Ocean in winter
In January 2018, Dr David McKee and Dr Ina Lefering from the Marine Optics and Remote Sensing Group (Department of Physics) set out on their first expedition to the Barents Sea (East of Svalbard) to study the impact of sea-ice thinning and early retreat on physical and chemical processes that underpin ecosystem function. The expedition is part of a series of research cruises to collect data for Arctic PRIZE, one of 4 main projects in the NERC-funded Changing Arctic Ocean Programme. The project is led by colleagues from the Scottish Association of Marine Science in Oban and has partners from the Universities of Edinburgh, St Andrews and Oxford. The major modelling effort is being directed by Dr Neil Banas from Department of Mathematics and Statistics, University of Strathclyde.
The Arctic is the fastest changing environment on the planet - sea-ice is retreating and getting thinner, while freshwater in-flow and temperatures are increasing. These changes will have a major effect on all life in the Arctic, in ways that are, at present, unknown or poorly understood.
All life in the Arctic Ocean, from sea floor to sea surface, has adapted to the extreme environmental conditions, such as very cold temperatures and extreme seasonal cycles in light availability. The rapid changes we have observed in recent years pose a serious threat to the balance of the entire Arctic Ocean ecosystem.
Arctic PRIZE focuses on the interplay between physical and chemical processes in the seasonal ice zone and how they combine to influence life in the water column and on the seabed. The seasonal ice zone is the transition between open ocean and sea ice. It is very dynamic, influenced by weather and seasons, and sea ice conditions can change from a solid ice cover to small isolated floes over periods of hours or days. It is also a region of high productivity during spring and summer, when sea ice melts and sunlight can penetrate the ocean. This, together with a stable, nutrient-rich layering of the surface ocean, leads to a spike in growth, and hence density, of microscopic algae through increased photosynthetic activity. The resulting huge algal bloom that forms every spring supports the marine food web – including zooplankton (microscopic grazers), sediment dwellers and the top predators, such as birds, seals, and whales – and polar bears.
Arctic PRIZE investigates different aspects of the seasonal cycle in productivity: (1) the physical properties of the water column (such as temperature, salinity, and light), (2) nutrient availability and dynamics, (3) phytoplankton productivity, (4) zooplankton response and behaviour, and (5) the impact on organisms living on and in the seafloor.
New data for the project is primarily being collected on 3 dedicated research cruises, the first recently completed in January, with the next two taking place in April and June / July – a total of 8 weeks at sea. The Marine Optics and Remote Sensing team is measuring light fields directly and collecting additional optical properties to support radiative transfer modelling of changing light fields across the seasonal cycle. Additional data from underwater gliders deployed to patrol the Barents Sea between research cruises and from ocean colour satellites will provide an unprecedented, time-resolved, 3D overview of primary productivity in this region.
Being just back from the first expedition, it is safe to say that making all of these measurements on a ship in the dark, stormy winter of the Barents Sea in January is a real challenge – and one of the reasons why we know so little about the Arctic Ocean in winter. 24h darkness, water temperatures of -1.8 C and (too many) polar lows producing 7 – 8m waves made for unusual working conditions. To make up for the less pleasant moments, we were very fortunate to see spectacular Northern Lights and watch both Humpback whales and Orcas feed in a beautiful Norwegian fjord – at the same time. Despite the difficult conditions, we managed to get interesting data showing incredibly low levels of biomass and extremely clear waters that provide a baseline for subsequent spring blooms after the sun eventually rises. We will report on that on our return to the Barents Sea in spring and summer when 24h daylight will also, hopefully, give us our first sight of a polar bear!
Dr Ina Lefering and Dr David McKee, Department of Physics, University of Strathclyde