Reconstructing modern and Pliocene (c. 5.4-2.4 Ma) decadal climate variations in the paleoenvironments of the Middle Atlantic Bight using isotope and increment sclerochronology

Ocean characteristics on geologic timescales are poorly understood, have varied in the past, and are critical to understanding how the ocean may respond to future human-induced climate change. Recent climate studies have identified that environmental variations in the Mid-Atlantic Bight (MAB) are related to larger global climate variations throughout the Late Cenozoic such as the Atlantic meridional overturning circulation pattern and ocean-atmospheric teleconnections. Modern physical oceanographic studies in the MAB using the modern instrument records show high interannual variability with longer, multi-decadal warming trends. The goal of this investigation is to reveal annual to multi-decadal variations in sea surface temperatures of the MAB during the Pliocene (5.4-1.8 Million years ago (Ma). This investigation employs isotope and increment records from marine bivalves as proxies for ocean bottom temperature in conjunction with a basic understanding of the modern physical oceanographic flow model along the Atlantic continental shelf.;In the present study, live-collected bivalves from the MAB and fossil bivalve shells from Pliocene deposits along the US Mid-Atlantic Coastal Plain (MACP) were used to estimate oceanic conditions (seawater temperature, salinity, etc.) and ocean/atmosphere internal oscillations that currently dominate the basin. Sclerochronologic and stable isotope analyses were used to study this problem. Using the growth increments and isotope records of the modern Hemimactra as a comparison, Pliocene surf clams were employed to estimate paleoecologic and paleoclimatologic conditions along with the MACP. Pliocene surf clams documented annual increment marks and oxygen isotope ratios indicating greatly reduced seasonality, similar to the modern S. s. similis, but with similar average temperatures relative to modern SST at the same latitude. Since the surf clams present within the Pliocene MACP represent the short-lived species (∼ 5 years old), in order to investigate multi-decadal variations during the Pliocene new bivalve proxies were explored. Large and abundant MACP bivalves, Glycymeris americana and Panopea reflexa were identified as having annual growth increments and significant longevity. Ages of fossil shells were comparable to extant species G. glycymeris (∼100 years) and were used to reconstruct regional SST and a spectral analysis of past NAO. Oxygen isotope values were consistent with previous bivalve studies.