Last Glacial Maximum to present paleoclimate and paleovegetation records from the North Island East Coast : selection for input into a climate-driven hydrological transport model

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Litchfield, N.J.; Page, M.J.; Upton, P.; Gomez, B.; Carter, L.; Vandergoes, M.J. 2011 Last Glacial Maximum to present paleoclimate and paleovegetation records from the North Island East Coast : selection for input into a climate-driven hydrological transport model. Lower Hutt, N.Z.: GNS Science.GNS Science report 2011/20 24 p.

Abstract: The transfer of sediment across continental margins is controlled by a number of factors. One way to quantitatively assess the relative influence of the different factors is through numerical models. As part of the MARGINS Source-to-Sink programme we are developing a climate-driven hydrological transport model (HydroTrend) to investigate evolution of the Waipaoa Sedimentary System in the North Island East Coast, New Zealand, over the past 22,000 years (i.e., since the Last Glacial Maximum). Two important model inputs are paleoclimate (paleoprecipitation and paleotemperature) and paleovegetation. In this report we summarise available proxy records from the North Island East Coast, and outline methods used to select and prepare records for input into the models. Twenty three paleoclimate and paleovegetation records were compiled and of these, 10 were selected as key and are described in more detail herein. The majority are pollen records, including marine core P69, which was used as the primary paleovegetation record on the basis that it is the longest and only record to span the Last Glacial Maximum (LGM). The top of core P69 appears to be missing, so the uppermost part of the regional paleovegetation record is interpreted from a core from Repongaere Swamp. Paleovegetation zones were converted to vegetation/erosion factors, which were then used as HydroTrend model inputs. An alkenone Uk’ 37 record from marine core MD97-2121 was selected to constrain the paleotemperature on the basis that it is the only regional temperature proxy record to span 22,000 yr BP. Paleotemperature data from MD97-2121 was used as a forcing factor to estimate a land surface temperature record between two fixed points – today’s temperatures and Drost et al.’s (2007) LGM climate model for the eastern North Island. Three paleoprecipitation records were derived by integrating modern records with proxy data from sediment cores. The first record is a coarse resolution, 22,000 year record derived by using MD97-2121 sea surface temperatures to estimate the precipitation between two fixed points – today’s precipitation and Drost et al.’s (2007) LGM climate model. The other two records were derived from high resolution sediment cores, and were determined from the Lake Tutira storm record using two alternative methods. One method used a relationship between storm sediment thickness and storm rainfall, and between storm rainfall and annual rainfall during the European pastoral period, to estimate paleostorm and paleoannual rainfalls, based on a sedimentation rate conversion factor under forest. The other method scaled the number of storms in each 100 year period to the modern rainfall record, by assuming that: i) the number of historic storms reflects the average annual rainfall, and ii) that those periods with the maximum and minimum number of storms equate with 2.0 and 0.5 times the contemporary average annual rainfall, respectively. All three paleoprecipitation records were input into the HydroTrend model and the results compared between them. (auth)