High-resolution Pleistocene diatom biostratigraphy of Site 983 and correlations with isotope stratigraphy

Abstract

High accumulation rates and the presence of well-preserved, abundant diatoms in Site 983 sediments from the Gardar Drift gave us the opportunity to refine the Pleistocene diatom biostratigraphic resolution of the high-latitude North Atlantic. Eight Pleistocene diatom datum events are identified and, for the first time, tied directly to the oxygen isotope record and paleomagnetic stratigraphy of Site 983. These datum events are (1) the last occurrence (LO) of Proboscia curvirostris at 0.3 Ma, (2) the LO of Thalassiosira jouseae at 0.3 Ma, (3) the LO of Nitzschia reinholdii at 0.6 Ma, (4) the LO of Nitzschia fossilis at 0.68 Ma, (5) the LO of Nitzschia seminae at 0.84 Ma, (6) the first occurrence (FO) of N. seminae at 1.25 Ma, (7) the FO of Proboscia curvirostris at 1.53 Ma, and (8) the FO of Pseudoeunotia doliolus at 1.89 Ma. Most of these datums are found to be synchronous between the middle and high latitudes of the North Atlantic and the North Pacific. On the basis of these datums, four highlatitude North Atlantic diatom zones are proposed for the Pleistocene. The record of diatom abundance and preservation at Site 983 gives evidence for the influence of fluctuating Pleistocene climatic conditions on diatom productivity in the high-latitude North Atlantic.

Expansion of subarctic water masses in the North Atlantic and Pacific oceans and implications for mid‐Pleistocene ice sheet growth

“…Site 983 is ideally positioned to register changes in the position of the Arctic Front and thus the extent of the Arctic water mass in the North Atlantic. This has been demonstrated in previous examinations of Site 983 sediments and of its closest neighbor, Site 984, using diatoms and foraminifera respectively [Koç et al, 1999;Wright and Flower, 2002]. The sensitive location of Site 983 may account for the high degree of variability in SSTs and %C 37:4 within glacial/ interglacial stages.…”

A major change in North Atlantic deep water circulation 1.6 million years ago

“…These authors concluded based on the absence of production of silica in the surface waters of the GIN seas relative to the region south of Iceland (Koç and Flower, 1998;Koç et al, 1999) that a strong front must have existed near the Greenland-Scotland Ridge during most of the interglacials of the early to mid-Pleistocene (summarized by Raymo et al, 2004). This was reflected by the presence of a pronounced low-δ 13 C water mass at mid-depth throughout the 41 kyr world ∼ 1.8-1.2 Ma.…”

Site U1307

“…Koç et al, 1999) is tentatively placed between Samples 303-U1307A-3H-CC and 4H-CC and 303-U1307B-3H-CC and 4H-CC (Fig. F12).…”

“…Peak numbers from 1 to 8 represent the location of the foraminifer ooze layers of Unit I. (Sato et al, 1999) Diatom datum (Koç et al, 1999) Planktonic foraminifer datum (Weaver and Clement, 1987) MIS (Wei, 1993;Sato et al, 1999) Figure F13. Site U1307 downcore relative abundance of calcareous nannofossils, planktonic foraminifers, diatoms, radiolarians, dinocysts, and pollen.…”

“…F12). The FO of this species (1.25-1.26 Ma, MIS 37; Koç et al, 1999) is implied between Samples 303-U1307A-6H-CC and 7H-CC and 303-U1307B-6H-CC and 7H-CC. These stratigraphic placements do not reflect the true LO and FO of the species.…”