Abstract
During the sea level lowstand of the Last Glacial Maximum, the entrance sills of the New Zealand fiords were above sea level. With de-glacial onset, stranded lakes developed behind the sills in the fiord basins, and as sea level rose, basins were flooded with marine water. The fiords are an example of ingression basins, which are a useful method for studying sea level rise because chronology and sea level elevation data are readily available. The impounding entrance sill is used to track the marine incursion into the basin, where sediment contains a dateable record of the lacustrine to marine transition. A wide range of paleo-sea level magnitudes are possible to find in Fiordland because the sill depths range from -30m to -120 m.
Using seismic data and sediment cores obtained in Fiordland on three cruises, the marine incursion is identified in seven fiords. In three of these fiords, six sediment cores reveal paleoenvironmental change from non-marine to marine using sedimentary facies analysis. Combining physical properties, visual observations, and microfossil assemblages, five sedimentary facies are identified. The vertical stacking of the sedimentary facies allows four fiord facies models to be developed. The facies models are then used to constrain the marine incursion and construct a relative sea level curve where chronology is compiled with radiocarbon dating. As a mid-latitude, far-field site in the Southern Hemisphere, a sea level curve from New Zealand is a valuable record from a location where only a few sea level records exist.
A relative sea level curve is constructed for Fiordland from -107m 14.9-14.2 ka to -43m 8.5-8.0 ka in a stepwise transgression. No direct evidence of Meltwater Pulse 1a is confirmed, but a pulse of sea level rise (at least 5 m) between 11.7-11.4 ka is identified as Meltwater Pulse 1b. Compared with other New Zealand sea level records, another pulse of sea level rise is identified between 9.8 and 7.0 ka culminating in the modern stillstand. The Fiordland curve is compared with global records to resolve the Southern Hemisphere as the dominant source of meltwater from 14-12 ka during the Antarctic Cold Reversal. Subsequently, the Northern Hemisphere was the main meltwater source from 10-7 ka.