Early to middle Miocene vegetation history of Antarctica supports eccentricity-paced warming intervals during the Antarctic icehouse phase

Recent palynological evidence from the upper section (< 664 mbsf) of the Miocene ANDRILL 2A (AND-2A) core in the Ross Sea indicated a brief warm period during the Mid Miocene Climatic Optimum (MMCO), during Antarcticaʹs icehouse phase. The nature of other Miocene climate fluctuations in Antarctica remains poorly resolved. Here, we present new palynological data from the lower section of the AND-2A core (> 664 mbsf) that reveal additional intervals of increased palynomorph abundance and diversity during the Antarctic early to middle Miocene. This evidence is consistent with a relatively dynamic early Miocene Antarctic icehouse climate with intervals of increased temperature and moisture, prior to the MMCO. Comparison with previous AND-2A studies indicates that periods of increased palynomorph abundance in the lower stratigraphic section largely coincide with ice sheet minima, distal ice conditions, and the presence of freshwater (i.e. increased precipitation, meltwater run-off, and freshwater ponds). Decreases in plant productivity mostly coincide with increased glaciation, decreased freshwater, and ice-proximal conditions during the Antarctic Miocene. Comparing the palynological data with other AND-2A data and global climate proxies (e.g., pCO2, δ18O, relative sea level, Milankovitch cycles) helps to resolve questions regarding the driving forces behind climate and vegetation change. We found that palynomorph assemblages reflecting generally warmer conditions are largely associated with 400-kyr eccentricity maxima, while assemblages indicative of colder conditions coincide with 400-kyr eccentricity minima. These data are consistent with other findings that indicate the early to middle Miocene climate was eccentricity-paced.