Oceanography Seminar Series: Dr. Igor Yashayaev
Dr. Igor Yashayaev
Bedford Institute of Oceanography, DFO
Title:
"The Combined Action of Stratospheric Polar Vortex Disruptions, Icelandic Low Displacements, and Extreme Arctic Sea Ice Losses Shuts Down Deep Convection in the Labrador Sea."
Time:
Tuesday October 17, 2023 - 11:45 AM to 12:35 PM Atlantic Time (Canada)
Also, come join us 15 min early (at 11:30 am) in the seminar room for coffee/tea/cookies, everyone is welcome!
Dr. Yashayaev will be presenting in person. Folks may also join by Zoom. (Details below)
Introduction:
Once in two-to-four years, I come to Dalhousie with an update of the full-depth Labrador Sea research. The time has come for another one. This time, however, I will try to change my habit of overloading a presentation, making it information-heavy and therefore not as effective as it could be if the information is spread between different means of sharing the content. Let us experiment with delivering the messages in stages. In the next paragraph, I tell what to expect from the talk. Then, I will ask you to contact me for a link to supporting material. In the last paragraph you will find the actual abstract, so you can start there to decide if the rest is of interest to you.
I usually start my presentations with an explanation why the region needs to be studied, and this part will not be sacrificed – those who do not respect the past will never make a respectful move into the future. This is also because I need to come up with a reason why I continue staring at the Labrador Sea after doing that for more than three decades of my life. Then, I gave a tour to everything taking place in the region on the scales from seasons to decades, sharing my excitement of convection being so active. Not this time! This part will see some reductions. The hardest decision is dropping the T-S diagrams, including the volumetric ones (Ooouch!!!). Some of this content can be found in the link I am happy to share. Only near the end of my past talks, when most of the audience felt so exhausted, had already fallen asleep or wisely fled, I would start murmuring something about the process. Not this time!!! The three key processes controlling convection, ventilation and the overall state of the Labrador Sea are a hit of the show. Of course, there are some critically important and strategic questions we may be able to address during the talk or in discussions. Like those concerning the recent game change in the Labrador Sea observational network as whole. Specifically, starting in the mid-2010s, the contributions of the annual ship surveys to the real-time, seasonal and annual assessments of oceanographic conditions in the Labrador Sea substantially declined. The omissions and deficiencies in the ship-based observations did not have any sensible impact on the completeness and accuracy of the reported variables (from 10 to 30 years ago I claimed totally opposite). The benefits of a game change like this are difficult to overestimate. It will allow to save or redirect funds, resources, manpower and ship time, and, last but not least, to substantially reduce the carbon footprint of the knowledge-building process. One of the most thrilling and eyebrow-raising question of the past pentad is of course – Can the Overturning in the Subpolar North Atlantic Program (OSNAP) be wrong about the Labrador Sea? My answer is very much positive here. Yes, there are many reasons why the OSNAP array is so likely to underrepresent and thus underestimate the contribution of the Labrador Sea to the Atlantic Overturning Circulation. Some of these reasons I touch in the manuscript offered to you fellow, but there are more reasons for that miss of a sea, and even though I will not raise it in the core talk, we can discuss and brainstorm it collectively before or after.
As mentioned, I have nearly finished the revision of the latest manuscript on the Labrador Sea oceanography, and as part of the presentation I will be happy to share it with all of you who are interested in the Labrador Sea research or just curious about it. It would be good if you find time to browse through the document in my Google Folder before, or even after, the talk. This will help to make our exchange more interactive during the talk, and have more take-home or bring-from-home messages. Please contact me, emailing to Labrador.Sea@gmail.com or igor.yashayaev@dfo-mpo.gc.ca or better both for a link to my Google Folder with the work you will be first to see and just a few of several stories we published in the past two years.
The abstract follows:
Labrador Sea Water, formed in Labrador Sea by winter convection occurring in cold winters, spreads across the ocean, renewing and ventilating its intermediate and deep layers. Historical ship-based and recent Argo float oceanographic measurements reveal cycles of multiyear intensification, deepening, relaxation and shutdown of convection. Increased winter cooling of 2012 initiated the last convective cycle. While the 2015 winter cooling was 1994-2023 high, convection reached 2000 m, its 1996-2023 deep, in 2018. The 2012-2015 winter mixing events caused by extreme surface cooling preconditioned the water column to be susceptible to deeper convection in 2016-2018, prolonging the convective deepening until 2018 and resulting in the largest and densest LSW class since 1995. Convection weakened afterwards. Its 2020-to-2021 and 2022-to-2023 shoaling of 800 m/year was the most rapid since the mid-1990s. The 2021 and 2023 convection depths of 800 m and 700 m, respectively, were the shallowest since 2010. In 2021, a southwestward shift of the Icelandic Low, weakened by a disrupted (stratospheric) polar vortex, slowed/reversed the westerly winds bringing warm air to the Labrador Sea reducing surface cooling and consequently convection depth to their long-term lows. In 2023, however, convective shutdown, leading to warming, oxygen loss and density decrease below 700 m, was caused by a massive upper-layer freshening. This and previous freshening events are lag-correlated with the extreme winter-to-summer Arctic sea ice losses. These processes and associated changes have significant implications to the Labrador Sea and subpolar North Atlantic ecosystems as a whole. The three periods of elevated oxygen content observed at the intermediate depths between 1990 and 2023, inclusively, resulted from the progressive development of winter convection during 1987-1994, 2000-2003 and 2012-2018. The oxygen content almost immediately responded to the respective convective shutdowns, last time in 2013.
Increasing spatiotemporal density of the Argo and, particularly, Deep Argo float observations combined with new methods of data quality control, calibration and synthesis provide accurate real-time year-round full-depth assessment of oceanographic conditions across the Labrador Sea, substantially reducing, if not eliminating, the need in infrequent seasonally-biased carbon-heavy ship-based observations for this purpose.
Location:
LSC, Classroom 3655
Oceanography Wing
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