Jm. Whitehead et al., Early Pliocene paleoenvironment of the Sorsdal Formation, Vestfold Hills, based on diatom data, MAR MICROPA, 41(3-4), 2001, pp. 125-152
Comparison of diatom data from modern surface sediments in Prydz Bay and th
e Kerguelen Plateau with diatom assemblages from the Sorsdal Formation, Ves
tfold Hills, indicates that the climate was warmer than present during the
early Pliocene (4.5-4.1 Ma). Extant, sea-ice associated diatoms are signifi
cantly less abundant throughout the Sorsdal Formation than in the modem Ant
arctic coastal zone. Extant diatoms in the Sorsdal Formation, including Ste
llarima stellaris, Thalassiosira oliverana, Fragilariopsis sublinearis, Pse
udo-nitzschia turgiduloides and Eucampia antarctica var. recta, are consist
ent with annual sea-surface temperatures (SST) of between -1.8 and 5.0 degr
eesC. The presence of S. stellaris indicates that the summer SSTs were >3 d
egreesC during some intervals. The absence of calcareous coccoliths and the
silicoflagellate Dictyocha suggests that the upper limit for summer SST wa
s <5<degrees>C. These data indicate that early Pliocene summer SST were bet
ween 1.6 and 3 degreesC warmer than today. Abundant Chaetoceros cysts infer
that stratified, open-water conditions were present during summer/spring.
Ice sheet models suggest that warming of the magnitude evident in the Sorsd
al Formation (less than or equal to3 degreesC) should have resulted initial
ly in increased snow accumulation and ice sheet growth. However, ice sheet
growth was probably short-lived, as the long-term response to this warming
in the early Pliocene resulted in a significant decrease in ice volume and
deposition of the Sorsdal Formation. Other factors, such as increased basal
-ice sliding and higher discharge (icebergs and melt-water), probably led t
o significantly elevated ablation rates from the Pliocene ice sheet, result
ing in ice sheet retreat. (C) 2001 Elsevier Science B.V. All rights reserve
d.