Dispatch 21: Shout Out!     Print

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David Jones and Andrey Proshutinsky

September 26, 2017

Weather: 100% cloudy, 30 knot winds with 45 knot gusts, light snow, rough seas

Temperature: 0 ˚C

Relative humidity: 93%

Location: Beaufort Sea, 74˚ 01’ N; 139˚ 56’ W

News

I want to start out today by saying a "Good Day eh" to Ms. McDonald's classes at Saint James Regional High School in Portauxeasque, Newfoundland. Ms. McDonald's father is Quartermaster, David Pike on the Louis S. St. Laurent and he was charged with transferring a collection of 85 Styrofoam cups (see photos) to the ship for the annual "shrinking of the cups". This ritual utilizes the daily CTD rosette casts to submerge the cups to depths of 1000+ meters where the pressure is well above atmospheric pressure. The big squeeze is put on the cups at those depths and the outcome is fairly amusing. Will post the results in a couple of days.

Soooo... We are back at Mooring Station D aka CB21 where, as predicted, the winds have picked up considerably and so have the waves. After an attempt to redeploy Mooring D, the plug was pulled on the operation and will be given another shot tomorrow. Meanwhile we shall steam to a couple of CTD rosette stations and get those casts completed. Waste not, want not, eh.

I love the word "steam" or "steaming" when used in the context of a ship getting underway. Chief Scientist, Bill Williams uses it all the time. With his strong British accent it gives the sense of really getting on with it!! Getting the days work done no matter what sort of impediments might stand in the way. When you are steaming along at 15 knots those impediments have no chance. Besides it sounds so much better than "dieseling" or perhaps "diesel-electric-ing" which would be a more accurate description given the Louis' current power-plant. There was a time before the conversion to the more fuel-efficient diesel-electric power-plant when the Louis had a steam based electric power-plant so "steaming" must be a holdover term. Actually there was a time when ships used coal-fired boilers to power steam engines like the early railroad locomotives had. So your ship really would steam along until it caught fire and sank–most ships were made of wood in the good old days.

The CTD rosette casts carry on unimpeded (mostly) by the winds and hunkered down in some of the ships labs is a whirlwind of chemical analysis activity. One of the analysis that is done on the ship is the Nutrient Analysis which is used along with several other parameters to study the ecosystem of the Beaufort Gyre. Sarah-Ann Quesnel (DFO-IOS) is the lead analyst for nutrients and uses a very cool tool to get the job done called a Segmented Flow Auto Analyzer (see photos). The machine uses a colormetric method (think Beers' Law again) to measure the concentration of nutrients dissolved in a seawater sample specifically nitrate, phosphate, and silicate. Her machine has the ability to analyze 30 samples per hour and since it is doing 3 different nutrients, it is making 90 measurements per hour something that would take Sarah-Ann at least 3 days to do manually. One consistent trend seen in these data is they all start at essentially zero at the surface (because that is where organisms are using them up), then they gradually increase to a depth of 150-225 meters. They then start to decrease and then stabilize once they hit a depth of about 400-500 meters (see Photo).

Beaufort Gyre Science

Question from Students: What causes the change of circulation of the Beaufort Gyre?

Answer: 1946-2003 period with more or less regular oscillation.

This is a very good question because knowing major factors and mechanisms responsible for the Arctic decadal variability allows us to predict behavior of the Arctic environment several years in advance. Here we repeat our diagram 15 from dispatch #14 (slide 11 here). This slide illustrates that if we know the type of an expected future regime, we can predict anomalies in atmospheric pressure distribution, trajectories of cyclones, precipitation and river runoff, sea ice conditions, prevailing oceanic circulation, freshwater and ocean heat content, and some anomalies expected in arctic ecosystems (see slide 11 for details).

In order to explain the alternation of cyclonic and anti-cyclonic regimes, we hypothesize that the Arctic decadal variability is regulated by heat and fresh water exchange between the Arctic Ocean and the North Atlantic (NA) with its seas (Greenland, Iceland, Norwegian and Labrador).

The interaction between basins is weak during anti-cyclonic circulation regimes and strong during cyclonic regimes. Slide 11 shows that during a cyclonic regime, the atmospheric cyclones penetrate to the Central Arctic and bring heat and moisture, while during an anti-cyclonic regime, the Arctic atmosphere is separated from the NA and the reduction of heat transport toward the Arctic results in Arctic cooling. At the same time, during an anti-cyclonic regime, the Arctic accumulates fresh water in the Beaufort Gyre (BG) region, while the NA experiences a fresh water deficit resulting in increased heat flux from the ocean to the atmosphere there. 

Regime shifts are controlled by the system itself through oceanic and atmospheric freshwater and heat fluxes that increase during the cyclonic regime and decrease during the anticyclonic regime. The chain of processes accompanying the decadal oscillations can be illustrated as following:

During the anti-cyclonic regime, the ocean accumulates fresh water through the increase of freshwater volume in the BG and through the increase of ice thickness and area due to enhanced ice growth. Consequently, the ice and water flux from the Arctic Ocean to the NA and the transport of Atlantic Water into the Arctic Ocean (as a compensation of outflow) are weaker than usual. Deep convection in the NA seas is then enhanced because the vertical stratification is reduced without fresh water in the surface layer. This decoupling of the NA seas from the Arctic leads to their eventual warming. The warming of the NA seas then intensifies NA cyclonic activity that results in the increased heat fluxes from the NA to the Arctic region. Warming of the Arctic establishes the cyclonic regime.

During the cyclonic regime, the Arctic Ocean releases fresh water to the NA. After several years of increased fresh water release to the NA, the surface layer there becomes cooler and fresher, and the ice extent increases in the Greenland Sea. Freshening associated with melting of the increased ice volume and increased flux of fresher surface waters leads to an increase in stratification and a decrease in the interaction between the deep ocean and the atmosphere; deep water convection is consequently suppressed and the interactions between the NA and the Arctic Ocean become weaker, reestablishing the anti-cyclonic regime.

In this sequence of processes, (“regular” climate decadal “oscillations”; Slide 12) the accumulation and release of fresh water plays a fundamental role in the interaction between the Arctic Basin and the NA and therefore, monitoring of fresh water changes in the Beaufort Gyre region by our project improves our understanding of the mechanisms of decadal arctic climate variability.