Climate change record in clam shells

Date:
December 13, 2021
Source:
Louisiana State University
Summary:
The tiny, pale surf clam about the size of a fingernail that most
people have seen and collected on beaches around the world holds
clues in its shell to Earth's past. For the first time, researchers
have been able to identify the monthly, and even weekly, ocean
temperatures recorded in these smooth clam shells. Because ancient
civilizations consumed these ubiquitous clams and left the shells at
archeological sites, researchers now have a new way to reconstruct
climate and its fluctuations from nearly 3,000 years ago.



FULL STORY ==========================================================================
The tiny, pale surf clam about the size of a fingernail that most people
have seen and collected on beaches around the world holds clues in its
shell to Earth's past. For the first time, researchers have been able to identify the monthly, and even weekly, ocean temperatures recorded in
these smooth clam shells. Because ancient civilizations consumed these ubiquitous clams and left the shells at archeological sites, researchers
now have a new way to reconstruct climate and its fluctuations from
nearly 3,000 years ago.


==========================================================================
"The equipment available now, compared to the past, is precise and
powerful enough to be able to reveal the sea surface temperature and
the overall climate at a specific location when the clam was building
its shell. This gives us archaeologists and paleoclimatologists another
tool in our proverbial toolbox to reconstruct past climate. As we know
today, climate can influence all kinds of practices and behaviors,
which may have been the case in ancient civilizations as well," said LSU Department of Geography & Anthropology doctoral candidate Jacob Warner,
who is the lead author on this new research published in Chemical Geology.

Warner and colleagues are focused on tracking a climate phenomenon
that affects a large part of the world called the El Nin~o Southern Oscillation, or ENSO, the warm phase of which is characterized by warmer
than normal ocean temperatures, increased rainfall and more tropical
storms and hurricanes in the southern U.S.

Warner's study sites are in northern Peru, which is one of the areas
most impacted by ENSO. The cold, deep water off the coast of Peru makes
it one of the most productive fisheries in the world; however, when a
warm ENSO event occurs, it can result in fishery die-offs.

To capture the sea surface temperature from different phases of ENSO,
the researchers collected 18 surf clams from markets and coastal beaches
in 2012, 2014 and 2016. This new research used a species of short-lived
surf clam called Donax obesulus, which has not been used to reconstruct
climate before. Previous studies have successfully used the short-lived intertidal clam species, Mesodesma donacium. However, this species is
now extinct in northern Peru.

Like trees and tree rings, clams create layers in their shells as
they grow.

Warner drilled along the shell to collect samples at each interval of
time during the clam's lifespan to get a snapshot of the ocean temperature
as the shell grew.

"Using the relationship between the chemistry of the shell and the ocean temperature, we found Donax obesuluscan record sea surface temperature
pretty well. With this information, we can push this back in time
and reconstruct what the temperature and climate was in the past,"
Warner said.

In a separate, forthcoming paper, Warner collaborated with fellow
archeologist Aleksa Alaica, a postdoctoral researcher at the University of Alberta to analyze the surf clam Donax obesulus found at an archaeological
site in the Jequetepeque Valley in northern Peru. They discovered that
the clams' shells were larger during warmer ENSO events; therefore,
shell size can also be used as a paleoclimate proxy. They also discovered
that the ancient people, who lived at this site, preferentially harvested larger individual clams, which indicates a fisheries management practice
in place more than 2,000 years ago.

Warner is currently reconstructing past climate using clam shells
collected at another archeological site called Cayla'n in the Nepen~a
Valley of north- central Peru that was occupied about 2,200-2,600
years ago.

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


========================================================================== Journal Reference:
1. Jacob P. Warner, Kristine L. DeLong, David Chicoine, Kaustubh
Thirumalai,
C. Fred T. Andrus. Investigating the influence of temperature and
seawater d18O on Donax obesulus (Reeve, 1854) shell d18O. Chemical
Geology, 2022; 588: 120638 DOI: 10.1016/j.chemgeo.2021.120638 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211213121904.htm

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