Late Glacial and Holocene Diatom Successions in the Gulf of Maine: Response to Climatologic and Oceanographic Change

Abstract

The diatom floras of a 16 meter long piston core from the Wilkinson Basin in the Gulf of Maine were analyzed quantitatively and their composition compared with diatom floras contained in surface sediment samples from the Canadian Arctic to Cape Harteras.

The very few and corroded specimens found in the lower portion of the core indicate that initial deposition from about 17,600 yrs to 13,500 yrs BP took place below a floating ice shelf. A Thalassiosira gravida — dominated flora occurs in two successive sharp peaks, about 12,500 and 10,500 yrs ago, indicating the presence of an ice-shelf edge or seasonally open sea ice, with nearly full glacial conditions in-between. This two-step deglaciation is reminiscent of the Younger Dryas and was probably brought about by the influx of glacial meltwater from the St. Lawrence. The end of glacial conditions is marked by a brief 50-fold increase in the abundance of diatom frustules and the dominance of Chaetoceros diadema, a species indicative of high biological productivity in coastal upwelling systems. During the remainder of the early Holocene the diatom floras were affected by dissolution and the residual flora (dominated by Paralia sulcata) is not suitable for paleoenvironmental interpretation. Beginning about 5,000 yrs ago, the diatom flora approached the composition of the modern Gulf of Maine flora, with the rising dominance of Thalassiosira eccentrica and accessory species, and the rise in frustule abundance. This ‘modernization’ is thought to be the result of the onset of tidal resonance within the Gulf of Maine.