Measurements

These are the things we are going to measure:

Salinity and Temperature

The backbone of oceanographic measurements is the so-called ‘CTD’, or Conductivity-Temperature-Depth measurements. By measuring these three properties simultaneously, one can infer the density of the water at that location. Typically, CTD profiles are taken from the surface to the bottom and from one side of a channel or ocean basin to the other side – at a regular spacing – so that a cross section of the water density is obtained. From this section the density-driven part of the flow can be calculated.

Sections taken with shipboard CTD-equipment will provide a snapshot of the water within Nares Strait at the time of the campaign. In addition, they will be used to calibrate the CT-measurements from moorings, as these instruments are known to ‘drift’ from their calibrated values over time (especially due to biological growth on conductivity sensors).

Flow velocity

The density-driven flow is only one part of the total throughflow. Other major constituents are forced by the tides and the winds. To get the complete picture, the actual flow velocity is measured with Acoustic Doppler Current Profilers (ADCPs), attached to underwater moorings at several locations across Nares Strait. These measurements provide information about, for example, the strength of the tides and the importance of the density-driven flow with respect to other components.

Chemical composition of the seawater

Trace chemicals in the seawater (oxygen-isotopes, dissolved oxygen, dissolved nutrients, barium) reveal some of the water’s hidden history. They give information about the origin of the water, its modification by mixing with water having different properties (and thereby the route is has taken from its origin to the place where the sample was taken), as well as ice formation and ice melting during its time in the Arctic Ocean. Trace chemicals are measured by taking water samples for subsequent processing in a laboratory.

Bathymetry (underwater topography) in Petermann Fjord

Very little is known about the bathymetry in Petermann Fjord. The fjord itself is at least 1000 m deep, while a sill of approximately 400 m deep is believed to separate the fjord from Hall Basin in Nares Strait. The echo sounder of the ship provides the opportunity to easily gather more depth measurements in relatively shallow water, while a low-frequency sounder will be used in deeper waters. The large calving events in 2010 and earlier this month may give us the opportunity to take depth soundings deep within the fjord in a part of the fjord that was previously hidden beneath the floating tongue of ice. Whether we will actually be able to do this strongly depends on ice conditions, in particular on the location of the recently-calved ice island.

Weather

The very strong winds observed in this area, arising because the air is pushed through the narrow gap between the high walls on either side of the channel, are important drivers for flow of ice and water in Nares Strait. Apart from their scientific relevance, they can also be hazardous for humans and aircraft affected by them. The weather in this area is monitored continuously from four automatic weather stations on islands along the coasts of Nares Strait. These weather stations will be serviced so that they can continue to record for another two years. The weather station data will be supplemented by shipboard observations during the campaign.

Ice thickness and drift velocity

For the majority of the year, the sea ice in Nares Strait is land fast (jammed in between the coasts). During a small window in summer, however, the ice bridges break up and the ice can move freely through the channel, allowing the thick multi-year Arctic ice to escape to the Atlantic Ocean. It has been very difficult so far to estimate the amount of ice that flows through Nares Strait, as satellites do a poor job at estimating sea-ice thickness (even though coverage estimates are fairly good nowadays). Both of these quantities are important for the volume flux, especially since the Nares Strait is known to contain much multi-year (and therefore thick) ice. We use moorings with ice-profiling sonar equipment that measure the thickness of the sea ice directly overhead. These in situ observations are of great importance, both for our current understanding of sea-ice conditions in Nares Strait, as well as providing validation data for satellite-based ice thickness products.