Thursday, August 30, 2018

Mysterious Zones of Antarctica - 2

Fig. 1a Southern Ocean
Fig. 1b Direction of ACC Flow
I. Background

In the previous post in this series the surface down to 125 meter depths of the seawater around Antarctica was featured.

Today, we will focus on the same general subjects of that discussion, except that we will focus on Antarctica seawater at depths greater than 125 meters down to 600 meters.

We focus on this area of the globe because it is becoming well known that the past managers at various institutions were wrong in their assessments of Antarctica, especially East Antarctica.

More about that later.

II. Its About The Seawater

The story about tidewater glacier dynamics is not so much about the ice on the vast ice sheet, rather, the focus has become a study of the nature of the Antarctic seawater, especially in the sense that it is becoming known as the main cause of sea level change caused by East Antarctica.

The Antarctic seawater is part of, and impacted by, the Antarctic Circumpolar Current (ACC):
"The Antarctic Circumpolar Current moves 140 million cubic meters (4.9 billion cubic feet) of water per second around Antarctica. That single current moves more water than all the rivers on the planet combined. The world's rivers move 1.3 million cubic meters (46 million cubic feet) of water per second."
(National Geographic, Antarctic Circumpolar Current). So, we are talking about a serious ocean current.

Remember that the Southern Ocean receives a serious share of the global warming that finds its way into the world's oceans:
"The vast Southern Ocean, which surrounds Antarctica, plays a starring role in the future of climate change. The global oceans together absorb over 90 percent of the excess heat in the climate system and roughly three-quarters of that heat uptake occurs in the Southern Ocean."
(Antarctica 2.0 - 3, quoting Climate Central, emphasis added). Here is more about Climate Central:
"To that end, an NSF-funded $21 million initiative called Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) run by Princeton University, and including Climate Central, MBARI, Scripps, University of Washington, University of Arizona and others, was launched in 2014 with the goal of deploying over a six-year period a fleet of autonomous, robotic floats, capable of observing the Southern Ocean (for the first time) year-round and across the entire expanse."
(Climate Central, emphasis added). Regular readers understand that this is a major scientific endeavor that we do well to keep an eye on.

III. Where Does The Less-Cold ("Warm") Seawater Come From?

Area A [West Indian]
Area B [East Indian]
Area C [Ross]
Area D [Amundsen]
Area E [Bellingshausen]
Area F [Weddell]
One of the factors we are considering in this series is "where does the less-cold ('warmer') deep water around Antarctica come from?"

There seems to be a changing narrative that seems to be engendered by a world ocean that is absorbing "over 90 percent" of global warming.

The changing narrative is to be expected because years ago the oceans were not absorbing that warming from the atmosphere, because global warming wasn't here yet.

Global warming came into existence a decade or so after the Industrial Revolution (circa 1750) but became a part of our public conversations many years later.

So, keep in mind (as you read older textbooks) that at some point the narrative changes simply because the climate began to change:
"There are two primary views concerning the stability of the East Antarctic Ice Sheet. One view, relying critically on the interpretation of Sirius Group glacial deposits in the Transantarctic Mountains, is that the ice sheet has been fluctuating dramatically throughout its existence and that it last disappeared during the Pliocene ∼3 Ma ago. By analogy with the warmer Pliocene, it is argued that the current ice sheet is susceptible to global warming. The other view, originating from marine and terrestrial work in the 1970s and 1980s is that the ice sheet has been stable for ∼14 Ma and that the continent has been subjected to unbroken, cold polar conditions subsequently. After summarising the status of the two hypotheses, we explain the rationale for this volume. Building on the Vega Syposium of April 1993, it presents the case for the stability of the East Antarctic Ice Sheet and includes new work on terrestrial geomorphology and geology, marine cores and ice-sheet modelling."
(Geografiska Annaler., Vol. 75, No. 4, 1993). That 1993 paper (25 yrs. ago) argues: move along folks, nothing to see here, East Antarctica is stable.

They were wrong.

Let's read some of the narratives that mention where the warmer seawater comes from:
"The mean ACC temperature ranges from -1 to 5°C, depending on the time of year and location. The mean surface salinity decreases poleward, in general, from 34.9 at 35°S to 34.7 at 65°S. Typical salinity values are between 33.5 and 34.7, poleward of 65°S. This Temperature-Salinity signature is due to a combination of water masses that meet in the Southern Ocean and are mixed and redistributed by the Antarctic Circumpolar Current. Following the inclined isopycnals, deep waters from the North Atlantic (NADW) are upwelled at the Antarctic Divergence, the current's southern boundary. As this water rises to the surface it mixes with and becomes Antarctic Surface Water (ASW). When the water mass reaches the near surface flow it is diverted northward by Ekman transport. This newly formed Antarctic Circumpolar Water (labeled by some 'modified NADW') travels north across the ACC until it reaches the convergence of the Polar Frontal Zone. Here, near surface Sub-Antarctic Water from the north mixes with the ASW and sinks to a mid-depth becoming Antarctic Intermediate Water (AAIW). While this mixing is taking place the geostrophic component of the ACC is translating the water eastward. The AAIW will continue north but, due to the 'West Wind Drift,' will be ejected into the Atlantic, Indian, and Pacific basins, where over time, it will be upwelled to the surface. The Antarctic Circumpolar Current is a critical component of the 'Great Ocean Conveyor Belt.'"
(Antarctic Circumpolar Current, emphasis added). The ACC, the largest ocean current on Earth, flows from west to east circling Antarctica (Fig. 1a, Fig. 1b).

IV. The Mixing Of Seawater

The ACC spreads seawater "from the north" all around Antarctica and into Area A through Area F (see Mysterious Zones of Antarctica and Antarctica 2.0 - 6 [& supplements A, B, C, D, E, F]).

As with the previous graphs, which show impacts that the mixing has on shallower 0-125 meter depths, the graphs in today's post detail the impacts that the mixing has on greater depths.

V. Conclusion

The impacts shown by the graphs tell the same story, which is that the Conservative Temperature (CT) changes are, in general, chaotic.

Temperatures at one depth at a given time will become warmer or colder than depths below and/or above them.

Whatever these temperatures are, previous posts have shown that the seawater involved in the mixing/warming have the potential to melt the colder ice of the glaciers they come in contact with (Hot, Warm, & Cold Thermal Facts: Tidewater-Glaciers, 2, 3, 4).

The next post in this series is here, the previous post in this series is here.

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