Recent Atlantic ocean warming unprecedented in nearly 3,000 years
UMass Amherst, Canadian research uses ancient lake sediments to extend
climate record

Date:
October 14, 2020
Source:
University of Massachusetts Amherst
Summary:
Sediments from a lake in the Canadian High Arctic allow climate
scientists to extend the record of Atlantic sea-surface temperature
from about 100 to 2,900 years. It shows that the warmest interval
over this period has been the past 10 years.



FULL STORY ========================================================================== Taking advantage of unique properties of sediments from the bottom
of Sawtooth Lake in the Canadian High Arctic, climate scientists have
extended the record of Atlantic sea-surface temperature from about 100
to 2,900 years, and it shows that the warmest interval over this period
has been the past 10 years.


==========================================================================
A team led by Francois Lapointe and Raymond Bradley in the Climate
System Research Center of the University of Massachusetts Amherst
and Pierre Francus at University of Que'bec-INRS analyzed "perfectly
preserved" annual layers of sediment that accumulated in the lake on
northern Ellesmere Island, Nunavut, which contain titanium left over from centuries of rock weathering. By measuring the titanium concentration in
the different layers, scientists can estimate the relative temperature
and atmospheric pressure over time.

The newly extended record shows that the coldest temperatures were
found between about 1400-1600 A.D., and the warmest interval occurred
during just the past decade, the authors report. Francus adds, "Our
unique data set constitutes the first reconstruction of Atlantic sea
surface temperatures spanning the last 3,000 years and this will allow climatologists to better understand the mechanisms behind long-term
changes in the behavior of the Atlantic Ocean." When temperatures
are cool over the North Atlantic, a relatively low atmospheric pressure
pattern is found over much of the Canadian High Arctic and Greenland. This
is associated with slower snow melt in that region and higher titanium
levels in the sediments. The opposite is true when the ocean is warmer -- atmospheric pressure is higher, snow melt is rapid and the concentration
of titanium decreases.

Lapointe says, "Using these strong links, it was possible to reconstruct
how Atlantic sea surface temperatures have varied over the past 2,900
years, making it the longest record that is currently available." Details appear this week in Proceedings of the National Academy of Sciences.

The researchers report that their newly reconstructed record is
significantly correlated with several other independent sediment
records from the Atlantic Ocean ranging from north of Iceland to
offshore Venezuela, confirming its reliability as a proxy for the
long-term variability of ocean temperatures across a broad swath of the Atlantic. The record is also similar to European temperatures over the
past 2,000 years, they point out.

Fluctuations in sea surface temperatures, known as the Atlantic
Multidecadal Oscillation (AMO), are also linked to other major climatic upheavals such as droughts in North America and the severity of
hurricanes. However, because measurements of sea surface temperatures
only go back a century or so, the exact length and variability of the
AMO cycle has been poorly understood.

Climate warming in the Arctic is now twice or three times faster than
the rest of the planet because of greenhouse gas emissions from burning
fossil fuels, warming can be amplified or dampened by natural climate variability, such as changes in the surface temperature of the North
Atlantic, which appear to vary over cycles of about 60-80 years.

Lapointe, who has carried out extensive fieldwork in the Canadian Arctic
over the past decade, notes that "It has been common in recent summers
for atmospheric high-pressure systems -- clear-sky conditions -- to
prevail over the region. Maximum temperatures often reached 20 degrees
Celsius, 68 degrees Fahrenheit, for many successive days or even weeks,
as in 2019. This has had irreversible impacts on snow cover, glaciers
and ice caps, and permafrost." Bradley adds that, "The surface waters
of the Atlantic have been consistently warm since about 1995. We don't
know if conditions will shift towards a cooler phase any time soon,
which would give some relief for the accelerated Arctic warming. But
if the Atlantic warming continues, atmospheric conditions favoring more
severe melting of Canadian Arctic ice caps and the Greenland ice sheet can
be expected in the coming decades." In 2019, Greenland Ice Sheet lost
more than 500 billion tons of mass, a record, and this was associated
with unprecedented, persistent high pressure atmospheric conditions."
Lapointe notes, "Conditions like this are currently not properly captured
by global climate models, underestimating the potential impacts of future warming in Arctic regions."

========================================================================== Story Source: Materials provided by
University_of_Massachusetts_Amherst. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Francois Lapointe, Raymond S. Bradley, Pierre Francus, Nicholas L.

Balascio, Mark B. Abbott, Joseph S. Stoner, Guillaume St-Onge,
Arnaud De Coninck, Thibault Labarre. Annually resolved Atlantic sea
surface temperature variability over the past 2,900 y. Proceedings
of the National Academy of Sciences, 2020; 202014166 DOI: 10.1073/
pnas.2014166117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201014140933.htm

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