Carbon isotopic equilibrium of the surface waters as a proxy for climate change through the last glacial/interglacial cycle in the Southwest Pacific

Abstract

Carbon-13 is a relatively understudied geochemical property in the world ocean. The Southwest Pacific, in particular, is devoid of δ¹³C data. This thesis therefore has two main objectives: to create a model to describe the modern distribution of δ¹³C around New Zealand (30-70°S, 140°E-150°W), and to describe changes in δ¹³C in a latitudinal transect of cores to the east and south of New Zealand. A model using multiple linear regression was created by comparing δ¹³C with potential temperature, salinity, density, and oxygen data. This model matches well with ship board δ¹³C measurements taken throughout the region. The resulting models were then compared to core top data to determine how well modern δ¹³C values compare to the Holocene, pre-industrial values. A new model, based on previous pre-industrial models, was created at much higher resolution to recreate the pre-industrial δ¹³C distribution. Core top values were found to be intermediate between Holocene and modern values. Down core δ¹³C data was split into six regions based on oceanographic conditions to determine what caused and how δ¹³C change occurred in the past. Data was run through 1000 iterations of a Monte Carlo simulation to determine a robust δ¹³C curve back through time. The biologic pump was found to dominate the δ¹³C levels in the region through iron fertilization and increased productivity in the polar zone. The LGM and deglacial δ¹³C values reflect greater influence on δ¹³Catm, suggesting that an increase in upwelling along the Antarctic coast and a possible strengthening of the westerly wind belt caused changes in ocean circulation throughout the region. The ACR and Early Holocene periods show good correlation with atmospheric CO₂ records, suggesting increasing temperatures may have increased productivity. The remainder of the Holocene to the present is mainly influenced by δ¹³Catm, suggesting relatively stable conditions in ocean and atmosphere.