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Author Topic: Where Does The Water Go?  (Read 292 times)

JimboOmega

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Where Does The Water Go?
« on: August 10, 2019, 12:05:25 AM »
On the DMI Greenland site, losses are often expressed in terms of Gigatons, which they explain as being equivalent to a cubic kilometer of water.  In a typical year, it seems like ~200 GT might melt, whereas in the worst years like this one, 300 or 400 GT might melt.

This is a tremendous amount , and it's very fresh water, assuming it melts and winds up in the surrounding waters. 300 Gt could cover the entire arctic ocean 2cm deep; or it could cover a million square kilometers 30 cm deep.

Does such a large impulse of fresh water actually impact the surrounding currents and oceans? In years where it's way more than climatology, what weird effects occur? Does the water go somewhere else (for instance, evaporating into the atmosphere)?  On some days, like recently, 10GT are removed in a day, do those pulses have impacts on other things in the cryosphere? Or are they mostly of concern only to the greenland ice sheet itself?

Cookymonster

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Re: Where Does The Water Go?
« Reply #1 on: August 10, 2019, 12:41:46 AM »
Great Question, beyond my skill set to answer - but I really look forward to the conversation!

Rich

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Re: Where Does The Water Go?
« Reply #2 on: August 10, 2019, 01:05:52 AM »
There has been a fair amount of study on this.

If you look at a multi-year temperature anomaly map of the globe, one region that has been reliably below the baseline average is the south of Greenland in the N. Atlantic. That's due to cold meltwater on the surface

The meltwater slows the AMOC as the fresh surface water infusion reduces the density of the surface water in the same N. Atlantic region where the AMOC sinks.

AMOC circulation has declined by 15-20% in the last 50 years. It's a big deal for a variety of reasons. Impact on weather and oxygenation of the ocean being two that come to mind.


KiwiGriff

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Re: Where Does The Water Go?
« Reply #3 on: August 10, 2019, 01:24:51 AM »
Greenland Ice Melt Could Push Atlantic Circulation to Collapse.
https://www.hakaimagazine.com/news/greenland-ice-melt-could-push-atlantic-circulation-collapse/
Quote
In the North Atlantic, east of North America and south of Greenland, the ocean’s upper layers are much warmer than one might presume given the extreme latitude. This unexpected warmth is a product of the Atlantic Meridional Overturning Circulation (AMOC), a vitally important system of ocean currents that moves warm salty water northward from the tropics and cold fresher water south. The AMOC looms large in the Earth’s climate: it is responsible for redistributing nutrients throughout the Atlantic Ocean and is a major driving force controlling the climate on both sides of the pond.

Ocean currents all experience fluctuations, which can dramatically change the distribution of nutrients, heat, and fish. The best known example is probably the El Niño-Southern Oscillation, in which unusually warm water occasionally disrupts the Pacific Ocean’s Humboldt Current that flows north from Chile toward Peru. El Niño events can shift the jet stream south, cause excessive rainfall and devastating floods, and temporarily collapse fish stocks.

To date, most climate research suggests that the AMOC is relatively stable and carries water throughout the ocean in a reliable, repeating cycle. But anthropogenic climate change seems to have made the current weaken slightly, raising the question of whether more dramatic shifts are in store. As of the most recent Intergovernmental Panel on Climate Change report, a shutdown of the circulation from further warming is considered unlikely. Yet a new study says that the unprecedented melting of Greenland’s massive ice sheets, previously overlooked in most climate modeling, will result in the AMOC weakening, and maybe even collapsing, within the next 300 years.
based on the paper.
Fate of the Atlantic Meridional Overturning Circulation: Strong decline under continued warming and Greenland melting
P. Bakker etal.2016
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL070457
Abstract
Quote
The most recent Intergovernmental Panel on Climate Change assessment report concludes that the Atlantic Meridional Overturning Circulation (AMOC) could weaken substantially but is very unlikely to collapse in the 21st century. However, the assessment largely neglected Greenland Ice Sheet (GrIS) mass loss, lacked a comprehensive uncertainty analysis, and was limited to the 21st century. Here in a community effort, improved estimates of GrIS mass loss are included in multicentennial projections using eight state‐of‐the‐science climate models, and an AMOC emulator is used to provide a probabilistic uncertainty assessment. We find that GrIS melting affects AMOC projections, even though it is of secondary importance. By years 2090–2100, the AMOC weakens by 18% [−3%, −34%; 90% probability] in an intermediate greenhouse‐gas mitigation scenario and by 37% [−15%, −65%] under continued high emissions. Afterward, it stabilizes in the former but continues to decline in the latter to −74% [+4%, −100%] by 2290–2300, with a 44% likelihood of an AMOC collapse. This result suggests that an AMOC collapse can be avoided by CO2 mitigation.

.Discussion by S Rahmstorf at real climate on a paper of his on same subject.
.http://www.realclimate.org/index.php/archives/2015/03/whats-going-on-in-the-north-atlantic/
What’s going on in the North Atlantic?

Quote
The North Atlantic between Newfoundland and Ireland is practically the only region of the world that has defied global warming and even cooled. Last winter there even was the coldest on record – while globally it was the hottest on record. Our recent study (Rahmstorf et al. 2015) attributes this to a weakening of the Gulf Stream System, which is apparently unique in the last thousand years.

The whole world is warming. The whole world? No! A region in the subpolar Atlantic has cooled over the past century – unique in the world for an area with reasonable data coverage (Fig. 1). So what’s so special about this region between Newfoundland and Ireland?
Fig. 1 Linear temperature trend from 1900 to 2013. The cooling in the subpolar North Atlantic is remarkable and well documented by numerous measurements – unlike the cold spot in central Africa, which on closer inspection apparently is an artifact of incomplete and inhomogeneous weather station data.

It happens to be just that area for which climate models predict a cooling when the Gulf Stream System weakens (experts speak of the Atlantic meridional overturning circulation or AMOC, as part of the global thermohaline circulation). That this might happen as a result of global warming is discussed in the scientific community since the 1980s – since Wally Broecker’s classical Nature article “Unpleasant surprises in the greenhouse?” Meanwhile evidence is mounting that the long-feared circulation decline is already well underway.

Impacts.
Global and European climate impacts of a slowdown of the AMOC in a high resolution GCM
C. Jackson et al.
Abstract

Quote
The impacts of a hypothetical slowdown in the Atlantic Meridional Overturning Circulation (AMOC) are assessed in a state-of-the-art global climate model (HadGEM3), with particular emphasis on Europe. This is the highest resolution coupled global climate model to be used to study the impacts of an AMOC slowdown so far. Many results found are consistent with previous studies and can be considered robust impacts from a large reduction or collapse of the AMOC. These include: widespread cooling throughout the North Atlantic and northern hemisphere in general; less precipitation in the northern hemisphere midlatitudes; large changes in precipitation in the tropics and a strengthening of the North Atlantic storm track. The focus on Europe, aided by the increase in resolution, has revealed previously undiscussed impacts, particularly those associated with changing atmospheric circulation patterns. Summer precipitation decreases (increases) in northern (southern) Europe and is associated with a negative summer North Atlantic Oscillation signal. Winter precipitation is also affected by the changing atmospheric circulation, with localised increases in precipitation associated with more winter storms and a strengthened winter storm track. Stronger westerly winds in winter increase the warming maritime effect while weaker westerlies in summer decrease the cooling maritime effect. In the absence of these circulation changes the cooling over Europe’s landmass would be even larger in both seasons. The general cooling and atmospheric circulation changes result in weaker peak river flows and vegetation productivity, which may raise issues of water availability and crop production.
https://link.springer.com/article/10.1007/s00382-015-2540-2