PaleoENSO reconstructions of the Holocene and Last Glacial Period
View/ Open
Date
30/06/2015Author
Driscoll, Robin Eleanor
Metadata
Abstract
In this study, specimens of Tridacna sp., which are reef dwelling bivalve molluscs and
have been shown to live up to 60 years, collected from the Huon Peninsula, Papua New
Guinea, were sampled for geochemical profiles. The Huon Peninsula is in the heart of
the Western Pacific Warm Pool (WPWP), which plays a key role in ENSO dynamics. The
uplifted reef terraces of the Huon Peninsula have been extensively studied, and are well
dated, which gives the opportunity to reconstruct the local climate of this region at key
intervals during the past.
Previous work on Tridacna sp. has shown that they precipitate their aragonite shell in
equilibrium with the surrounding seawater, and the δ18O profile of a modern T. gigas
from the Huon Peninsula has been shown to correlate with precipitation and
temperature anomalies, and the Niño 3.4 temperature anomaly record. Fossil samples
from this region are therefore assumed to have the ability to capture changes in δ18O
attributable to ENSO.
Seasonally resolved δ18O measurements from Tridacna sp. from early Holocene and
Marine Isotope Stage 3 (MIS3) reefs were used to reconstruct changes in mean climate,
seasonality and inter-annual variability (e.g. ENSO). Reconstructions of the mean state
tend to agree with previously published studies of Holocene and MIS3 climate, showing
similar temperatures to today during the early Holocene, and an average cooling of 2-
3°C during MIS3. The early Holocene Tridacna sp. samples show a reduction in
seasonality, consistent with the reduction in seasonal insolation at this time, while
those from MIS3 show variable seasonality between 30-60ka. ENSO appears to have
been supressed during the early Holocene by up to 50% compared with the late 20th
century, which is consistent with coral data and modelling studies. During MIS3, ENSO
appears to have been more variable with some records showing anomalous warm and
cool events as strong as those seen in the modern T. gigas, used here as a benchmark.
Trace element profiles derived from the Tridacna sp. used in this study show a
tentative link with temperature and local productivity, but these relationships are
subject to species specific and intra-shell effects.