Warm water dominates Svalbard fjords
Seawater temperature measured from December 2011 to December 2012 shows that warm water still dominates Svalbard fjords. This is of vital importance for the sea ice cover this winter. Measurements done continuously in Adventfjorden and Billefjorden monitor the development in the water column and the hitherto unknown biological activity in the Polar night.
Ever wondered why you observe light out in Adventfjorden every week? And why people go out in zodiacs in the middle of the cold, dark winter? The answer is that biologists and oceanographers at UNIS are monitoring the water column in Isfjorden to see any changes and how this affects the life in the ocean.
Monitoring programs in the fjords
Throughout the last year we have collected samples of sea water, microorganisms and zooplankton every week in Adventfjorden outside Longyearbyen and once a month in Adolfbukta in Billefjorden.
In order to gain coherent information about the state of the ocean, we have also deployed several ocean observatories, anchored to the seafloor and with instruments that every 10 minutes record sea temperature, salinity, currents and light conditions. One of the observatories has been located in Isfjorden since 2010, one in Adolfbukta since 2008, two in Kongsfjorden since 2002 and one in Rijpfjorden on Nordaustlandet since 2006.
UNIS leads several large research programs that have started up in the last two years: AWAKE, MicroFun, CLEOPATRA II and CircA. They all monitor the seasonal variations in the ocean, especially the biological processes during the dark season which are virtually unknown. Until now there have been few sampling expeditions and observations done during the polar night. UNIS has the unique opportunity to do something about this as we are present here during the whole winter.
Warm water in Isfjorden
Measurements of temperature and salinity in Isfjorden and its adjacent fjords, such as Adventfjorden and Billefjorden, show that the fjords are still dominated by warm water. Warm water is not uncommon this time of year, however, the important difference this year is that the warm water appears quite high in the water column, about 60-70 meters below the ocean surface.
In order to explain this phenomenon, we need to look back at the beginning of 2012. In January and February last year the prevailing winds were from the south, which brought warm and wet air to Svalbard.
Southeasterly winds blowing parallel to the west coast of Spitsbergen result in changes in the sea current pattern on the continental shelf. The warm Atlantic water in the West Spitsbergen Current (which is the northernmost leg of the Gulf Stream), is thus forced onto the continental shelf and all the way into Isfjorden.
The first sign of this air-ocean process is observed in mid-January 2012, when the Isfjorden observatory recorded an increased amount of warmer and saline water from the West Spitsbergen Current. In Kongsfjorden we see the same signal a few weeks later, in the beginning of February 2012.
A month after the first signs of warmer water in outer Isfjorden, we see the same warm water in Adventfjorden too Data from our weekly sampling in Adventfjorden (figure 1) show clearly that the cold water that previously dominated the water column, now is completely replaced by warm water. This warm water has lingered on in the fjord system ever since. The cold weather we had in April and May 2012 managed to cool the water surface to almost 0°C before the thawing season started.
During autumn 2012 the surface water started to cool again (figure 1), but there is still warm water with a temperature of more than 3°C close to the bottom of Adventfjorden. This is caused by episodic influx of warm water from Isfjorden into Adventfjorden.
Sea ice or no sea ice?
In September 2012, satellite images showed that the Arctic sea ice cover reached a record minimum in modern times. The major reason is that the ice thickness has been reduced over several years and thus melts more easily during summer.
Episodes with prolonged southern winds are another reason for reduced ice extent and ice thickness in the Arctic. The southern wind will push the sea ice northwards, bring along warm air and keep the ocean north of Svalbard warmer during winter. The reason for these prolonged southerly wind periods is low pressure systems that hit Svalbard instead of passing over the Barents Sea. This has happened more frequently in the month of January over the past couple of years. In other words, what happens in the atmosphere in January and February is of vital importance for the sea ice cover around Svalbard.
Regular observations done in Billefjorden help us follow the possible development of sea ice in the fjords. Figure 2 shows the temperature development from November until December 2012. In this period Svalbard experienced cold, stable weather conditions. The sea water close to the surface is below 0°C, but below 50 meters depth there is a warm water reservoir which could potentially migrate upwards in the water column and delay the cooling process.
Billefjorden is a sill fjord with less exchange of water masses. Adventfjorden has no sill/barriers and warm water from Isfjorden has direct access to the fjord (figure 1).
Looking at the temperature profile in Billefjorden on December 4, 2012 (figure 2) and assuming an air temperature of -10°C, a 10 m/s wind, and no input of warm water, it will take about 20 days before the surface water will reach the seawater freezing point. Unfortunately the wind will contribute to vertical mixing of warm water into the surface layer, especially now that there is a lot of warm water in Isfjorden and out on the continental shelf. In other words, there seems to be a poor chance of a solid sea ice cover in Isfjorden. The wind conditions in January and February will be decisive in such respect.
Biological activity in different water masses
As mentioned, Billefjorden is a sill fjord with generally less water exchange, local cooling of the water masses and usually good sea ice conditions. We therefore use the bay Adolfbukta in Billefjorden as a model system to study what happens in a typical Arctic fjord. Due to the limited water exchange in Adolfbukta we can assume that we are sampling the same population of zooplankton throughout the whole year.
In the CLEOPATRA II project we monitor the development and seasonal behavior of the copepod Calanus glacialis. This copepod can constitute as much as 90 per cent of the entire zooplankton system around Svalbard and is a very important food source for fish, sea birds and whales.
Adventfjorden, in contrast, is a very open and dynamic system regularly influenced by warm water influx from Isfjorden. In the MicroFun project we collect samples on a weekly basis to study what microorganisms appear in the different water masses and what roles they have in the marine food chain.
The water masses, the presence of microorganisms and zooplankton and the sea ice cover in the fjords are elements that are closely linked. In the different research programs within marine biology we are looking forward to follow the development this winter through different UNIS monitoring programs.