ASLR,
How would " increased freshwater inflow into the Arctic Ocean ... work to destabilize the halocline in that ocean"? I've read elsewhere (other ASIF threads, and maybe this one, too) that rivers (dumping fresh water into the Arctic) support the reestablishment of the halocline where storms and currents have somewhat mixed the top 30 or 50 meters.
Tor,
While you are correct that increasing influx of fresh riverine water into the Arctic Ocean increases the thickness of the halocline layer; which reduces heat flux from the Atlantic layer to the Arctic atmosphere.
Nevertheless, as the first linked reference cites, excess fresh surface water is frequently heated in the northern Chukchi Sea and then stored in the interior of the Beaufort Gyre. So more freshwater discharge into the Arctic Ocean will increase the heat stored in the Beaufort Gyre; which when released (during a temporary reversal of the Beaufort Gyre) will melt large areas of Arctic sea ice; which, will destabilize the halocline releasing more heat from the Atlantic layer into the Arctic atmosphere thus accelerating Arctic Amplification.
Mary-Louise Timmermans, John Toole and Richard Krishfield (29 Aug 2018), "Warming of the interior Arctic Ocean linked to sea ice losses at the basin margins", Science Advances , Vol. 4, no. 8, eaat6773, DOI: 10.1126/sciadv.aat6773
http://advances.sciencemag.org/content/4/8/eaat6773Abstract: "Arctic Ocean measurements reveal a near doubling of ocean heat content relative to the freezing temperature in the Beaufort Gyre halocline over the past three decades (1987–2017). This warming is linked to anomalous solar heating of surface waters in the northern Chukchi Sea, a main entryway for halocline waters to join the interior Beaufort Gyre. Summer solar heat absorption by the surface waters has increased fivefold over the same time period, chiefly because of reduced sea ice coverage. It is shown that the solar heating, considered together with subduction rates of surface water in this region, is sufficient to account for the observed halocline warming. Heat absorption at the basin margins and its subsequent accumulation in the ocean interior, therefore, have consequences for Beaufort Gyre sea ice beyond the summer season."
&
Also, the second linked reference indicates that in addition to the freshwater accumulated in the Beaufort Gyre the entire Arctic Ocean surface layer has been accumulating atypically high volumes of freshwater that are only recently beginning to leak atypically high volumes of freshwater into the North Atlantic. This implies that for many years now the full impacts of unusually high (anthropogenically driven) discharges of freshwater into the Arctic Ocean (and then on to the North Atlantic) have been masked. As thick layers of freshwater in the Arctic Ocean reduce the rate of heat flux from the deeper/warming layers of ocean water into the Arctic atmosphere, this atypically high accumulation of freshwater in the Arctic Ocean surface layers implies that in recent years the Arctic has been cooler than it otherwise would have been (without this atypically high accumulation). Thus if/when the Beaufort Gyre finally reverses it will likely not only release excessively high freshwater volumes accumulated in the Gyre into the North Atlantic, but it would likely also flush excess freshwater from the atypically high accumulations from the ocean surface layers in much of the Arctic Ocean and would likely melt large portions of the existing sea ice; which, would flush even more freshwater into the North Atlantic where this additional freshwater flux would serve to rapidly slow the AMOC:
Alexandra Jahn and Rory Laiho (27 July 2020), "Forced Changes in the Arctic Freshwater Budget Emerge in the Early 21st Century", Geophysical Research Letters,
https://doi.org/10.1029/2020GL088854https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL088854?af=RAbstractArctic liquid freshwater (FW) storage has shown a large increase over the past decades, posing the question: Is the Arctic FW budget already showing clear signs of anthropogenic climate change, or are the observed changes the result of multi‐decadal variability? We show that the observed change in liquid and solid Arctic FW storage is likely already driven by the changing climate, based on ensemble simulations from a state‐of‐the‐art climate model. Generally, the emergence of forced changes in Arctic FW fluxes occurs earlier for oceanic fluxes than for atmospheric or land fluxes. Nares Strait liquid FW flux is the first to show emergence outside the range of background variability, with this change potentially already occurring. Other FW fluxes have likely started to shift but have not yet emerged into a completely different regime. Future emissions reductions have the potential to avoid the emergence of some FW fluxes beyond the background variability.
Plain Language SummaryThe surface waters of the Arctic Ocean are fresher than the rest of the world oceans, due to the input of large amounts of river runoff. The very fresh surface ocean affects the ocean circulation and climate not just in the Arctic Ocean, but also at lower latitudes, especially in the North Atlantic. The last two decades have seen a freshening of the surface Arctic Ocean, for reasons that are currently unknown. Here we demonstrate that this freshening is likely already driven by climate change. Furthermore, we find that due to man‐made climate change, Arctic freshwater fluxes to the North Atlantic are also likely to soon start showing signs of change beyond the range of the variability we have observed in the past. The information provided here about the expected timing of the emergence of climate change signals will allow us to monitor upcoming changes in real time, to better understand how changes in the Arctic Ocean can impact climate worldwide.
Key points• The observed increase in Arctic liquid freshwater (FW) storage is likely already driven by climate change
• A forced change in liquid FW flux through Nares Strait is likely to emerge within the next decade
• The already changing nature of many FW budget terms can delay detection of shift and emergence from observations
Best,
ASLR