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Characterizing the Beaufort Gyre in the Canadian Basin of the Arctic Ocean from Satellite Observations Between 2003-2014

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Characterizing the Beaufort Gyre in the Canadian Basin of the Arctic Ocean from Satellite Observations Between 2003-2014 Characterizing the Beaufort Gyre in the Canadian Basin of the Arctic Ocean from satellite observations between 2003-2014 Heather Regan, Camille Lique Laboratoire d’Océanographie Physique et Spatiale IFREMER, Brest, France Thomas Armitage JPL, CalTech, Pasadena, USA Ocean Salinity Science – November 2018 Background: Arctic Freshwater • The Arctic Basin stores a large amount of freshwater (FW) • Most1.3 Water of the Masses storage and Circulation occurs in the Beaufort Gyre 7 120oE 120oE (a) 90 (b) 90 o E o o E o E E 150 150 60 60 o W o W o o E E 180 180 W W E E o o o o 30 30 150 150 120 120 o o o o W W 0 0 90 90 o o W o o W W W 30 30 60oW 60oW 27 29 31 33 35 0 5 10 15 20 Sea SurFace Salinity Salinity FW content (Freshwater ContentSreF = 34.8) (m) from MIMOC climatology from MIMOC climatology Figure 1.3: (a) Sea surface salinity and (b) liquid freshwater content (FWc) from MIMOC. The freshwater content is calculated by vertically integrating the salinity anomaly (Equation 1.1) from the surface to the depth of the 34.8 psu isohaline. The black box in (b) marks the location of the Beaufort Gyre as defined by Proshutinsky et al. (2009) and Giles et al. (2012). It is the single largest region of freshwater storage in the Arctic and will be discussed in more detail in Chapter 2. The white contour in (a) marks the location of the 34.8 psu isohaline. Dickson et al., 2007,andRawlins et al., 2010), with the most recent budget constructed by Haine et al. (2015). It must be noted, however, that whether the budget is now fully constrained, and whether any surplus/deficit in the supply/export of freshwater to/from the Arctic is significant is still a matter of debate, especially given that the observations of the di↵erent components of the freshwater budget vary considerably both in quality and in the period of time over which they were taken. Here, an average freshwater budget is presented based on the most robust and up-to-date observations of each component. In order of importance, freshwater in the Arctic is sourced from river runo↵,inflow through Bering Strait (Figure 1.4), and excess precipitation over evaporation. Based on the observations of Shiklomanov (2010) and the ERA-Interim reanalysis product (Dee 3 1 et al., 2011), river runo↵ accounts for an average input of 3900 390 km yr− . This rep- ± resents approximately 11% of the total global continental river runo↵ (Fichot et al., 2013), and is driven by the net precipitation that occurs over the Arctic catchment area due to the convergence of water vapour in the atmosphere above 50◦N(Serreze et al., 2006). JAHN AND HOLLAND: MOC IMPACTS OF ARCTIC CHANGES 3.2. Arctic Freshwater Export [6] The large simulated changes in the Arctic sea ice extent and volume have aBackground: wide range of impacts,Arctic Freshwater exports but here we concen- trate on the resulting changes in the Arctic FW export and the downstream impacts on the deep water formation (section 4). (a) As shown in Figures• 1eLarge–1g, the amount impact on theof simulated freshwater FW released to the N. Atlantic (ice + liquid) export to the NA through the two main pathways (Fram Strait and CAA) is a shift• towardEffect more on and SSS more downstream, FW export in the and potentially deepJAHN convection AND HOLLAND: MOC and IMPACTS AMOC OF ARCTIC CHANGES liquid phase, as well as a general increase in the total FW he export. The simulated phase change of the FW export is (a) (e) important for downstream effects, as the FW in liquid and solid form reaches different regions (see section 4). (b) CO2 increases [7] The large increase in the liquid FW export in RCP8.5 reflects a significant fresheningJAHN of the AND out HOLLAND:flow between MOC the IMPACTS OF ARCTIC CHANGES early 21st century and the early 23rd century (by 2.5 psu eshwater System with the major ocean 3.2.in Fram Arctic Strait Freshwater and 4.5 psu Export in the CAA). Between 2005 and 2200, this freshening of the Arctic Ocean (Figure 1h) is [6] The large simulated changes in the Arctic sea ice extent (b) (f) andcaused volume by have increased a wide sea range ice of melt impacts, within but here the we Arctic concen- and b FW export tratereduced on the sea-ice resulting formation changes and in the export Arctic (53%), FW export as well and as the by (c) ays in Fram Strait, the Barents Sea Opening, increases increased FW input from rivers (28%), an increase in the downstream impacts on the deep water formation (section 4). (a) FW import through Bering Strait (16%), and increased net denoting inflow and blue denoting outflow), the As shown in Figures 1e–1g, the impact on the simulated FW precipitation (2%) due to a generally enhanced hydrological he All Arctic Regions (ARR) definition of the export to the NA through the two main pathways (Fram Strait (B) summary of components of the high-latitude cycle in a warmer climate. and CAA) is a shift toward more and more FW export in the [8] While the salinity of the outflow decreases, the volume [this issue]. Here moisture is transported from t 89 liquid phase, as well as a general increase in the total FW fic Ocean via the Trade Winds over Central of the liquid FW export through the CAA and Fram Strait in parates the thermally stratified subarctic oceans export. The simulated phase change of the FW export is SSS and MLD RCP8.5 declines by up to 50% during the late 21st and the (c) an (lighter blue) in both(g) the Atlantic and Pacific important for downstream effects, as the FW in liquid and decreases mid 22nd century, respectively. For the CAA, the impact (d) nd Atlantic oceans to the Arctic catchment basins solid form reaches different regions (see section 4). (b) Prowse et al. k blue arrows), which subsequently drains into of the decrease in the volume export can be seen around ads initially within the Riverine Coastal Domain 2100[7] The as an large intermittent increase reductionin the liquid in the FW RCP8.5 export in liquid RCP8.5 FW reflects a significant freshening of the outflow between the waters (thin red arrows) enter the Arctic Ocean export in Figure 1g. It is caused by the shutdown of the deep rough the Barents Sea Opening (the Barents Sea early 21st century and the early 23rd century (by 2.5 psu convection in the Labrador SeaSurFace circulation at this time (see section 4) Schematic Maps of: (A) the domain of the Arctic Fr in Fram Strait and 4.5 psu in the CAA). Between 2005 and MOC decreasesubsurface,ridge cyclonic, system. topographically-steered Internally modified Atlantic and the associated rise in sea surface height in the Labrador Strait along eastern Greenland. Cooler and 2200,Sea, which this freshening reduces the of sea the surface Arctic Oceanheight gradient (Figure 1h) to the is caused by increased sea ice melt within the Arctica and (d) (h) Arctic that drives this export (see Jahn et al. [2010] and Jahn & Holland ter the Arctic Ocean through Bering Strait, and reduced sea-ice formation and export (53%), as wellFigure as 2. by (e) am Strait along eastern Greenland. Within the Houssais and Herbaut [2011]Carmack for detailset al. (2016) of this mechanism).currents (long arrows), the four Arctic(c) Ocean gatew (2013) increasedThis decrease FW in input the CAAfrom riversliquid FW (28%), export anleads increase to a in sharp the een inflow, interior and outflow shelves [cf. FW import through Bering Strait (16%), and3099 increased netDavis Strait and Bering Strait (think bars with red increase in the Arctic liquid FW storage after 21003100 (Figure 1h). gyral circulation patterns (circular arrows), and t precipitationFor Fram Strait, (2%) the due volume to a generallyflux decrease enhanced is fully hydrologicalcompensated terrestrial contributing areas shown in white; and cycle in a warmer climate. 3101 by the freshening of the outflow, so it cannot be seen3102 in freshwater system as introduced in 2015]. 8 fl Figure[ ] While 1e. It the occurs salinity around of the 2145, out ow after decreases, the shutdown the volume of the3103 subtropical and tropical Atlantic Ocean to the Paci of the liquid FW export through the CAA and Fram Strait in 3104 America (thick blue arrow). The subarctic front se deep convection in the Nordic Seas, and is caused by the asso- Figure 1. Time series of the (a) annual CO forcing in the CMIP5 RCP simulations, the Arctic sea ice extent in (b) (darker blue) from the salt-stratified Northern2 Oce RCP8.5ciated sea declines surface by height up to 50% gradient during change the late across 21st the and East the 3105 September(f) and (c) March, the annual Fram Strait (e) liquid and (f) solid FW export, (g) the annual CAA liquid and solid midGreenland 22nd century, current afterrespectively. deep convection For the CAA, ceases the (see impactJahn 3106FW export(d) (as markedoceans. in Moisture the panel), is transported and (h) from the the annual Pacific meana Arctic FW storage (liquid FWBluhm in the et topal., 250 m and solid by the mid-latitude (Westerlies) storm tracks (thic ofet theal. [2010], decrease for in details the volume of this mechanism). export can be seen around FW,3107 as marked in the panel). Figure 1d shows the 20 year running mean of the sea ice extent from Figures 1b and 1c versus the increasing3108 CO2 forcing inthe one Arctic ensemble Ocean (thick member white arrows) of the where RCP it simulations.spre The 20 year running mean is used to smooth 2100 as an intermittent reduction in the RCP8.5 liquid FW out the interannual variability, which we do not expect to be forced by CO .
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