Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology September 1995
Description:
Until now there has been no tool comparable to corals for reconstructing long term high-resolution
geochemical time-series for the colder, higher-latitude oceans. In this thesis, the
long-lived (+100 years) boreal mollusc (Bivalvia) Arctica islandica is shown to be practical
for this purpose in the northern North Atlantic Ocean. The evidence, compiled here,
demonstrates that the carbonate shell of this species faithfully records the ambient dissolved
inorganic carbon's (DIC) radiocarbon (Δ14C) concentration and accurately reflects the
ambient temperature in its stable oxygen isotope (δ180) composition. However, the stable
carbon isotope (δ13C) composition of the A. islandica shell likely is not a good recorder of
ambient DIC δl3C, and likely responds to physiological controls. Four Δ14C time histories
are reconstructed from the annual bands of A. islandica shells for the higher-latitudes of the
northern North Atlantic Ocean (from 41°N to 70°N). These ocean records show significant
spatial and temporal differences in the evolution of the radiocarbon signal between the
subpolar and subtropical regions and between eastern and western regions of the northern
North Atlantic, which are attributed to regional differences in mixed-layer depth and the
presence of deepwater sources. A 109-year interannual record of bottom temperatures for a
location near the former Nantucket Lightship position has been reconstructed for the period
1875-1983 from the overlapped stable oxygen isotope composition of four A. islandica
shells. This record's annual temperature anomalies (variation from the running ten-year
mean) show significant positive correlation with regional bottom, sea surface and air
temperature anomalies. However, the shell-derived bottom temperature record describes a
century-long cooling (~1°C) in contrast to a century-long warming of regional sea surface
temperatures of equal magnitude, indicating a long term divergence between surface and bottom conditions. It is suggested that this contrast may be owed to a reduction in vertical
mixing and increased seasonal stratification of shelf waters. This thesis fulfills the
prophesy laid out nearly two decades ago by Thompson and Jones [1977] that Arctica
islandica could someday be used to reconstruct past ocean history as "the tree of the North
Atlantic".
Description:
Funding was partly provided by an ORAU Global Climate Change Fellowship.
Keywords:
Clams
;
Paleoclimatology
;
Ocean quahog
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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