The South Pacific Convergence Zone (SPCZ) is the most prominent rain feature of the Southern Hemisphere, but is a very understudied region. Changes in the SPCZ can affect freshwater availability to people living on the islands in the South Pacific. The satellite record shows precipitation patterns from the past 37 years; in the tropics the best way to investigate rainfall before 1979 is to examine lake sediment. We used sediment cores with age models from Barora Lake, a shallow freshwater lake in the Solomon Islands, to obtain a detailed view of past rainfall patterns. This lake’s lack of oxygen one meter below the water’s surface has left its sediment in a uniquely undisturbed state. Because of this, and a high accumulation rate, the sediment provides a record of the rainfall in the Solomon Islands over the last millennium. Lipids are well-preserved in sediment over geologic time, making them an ideal proxy for reconstructing tropical paleoclimate. The lipid dinosterol is produced primarily by a limited group of dinoflagellate microalgae and acts as a “molecular fossil”. The isotopic ratio of deuterium to hydrogen (2H/1H) found in dinosterol reflects the 2H/1H ratio in the lake water, which is dictated by changes in precipitation and evaporation. In the tropics, more rain results in 2H-depleted rain and lake water. After purifying dinosterol from the sediment with column chromatography and high-performance liquid chromatography, we found minor fluctuations in the dinosterol 2H/1H ratios, which implies a fairly stable rainfall pattern at this location during the past millennium.
 

Anthropogenic carbon dioxide (CO₂) has been identified as a primary driver of climate change, the oceans have been shown to be a large sink of this CO₂. Fjord systems have been identified as potential sinks for the CO₂ in summer due to high primary production, but also in winter due to cool surface waters. Our study focuses on the temperate fjord system of Nootka Sound, BC, Canada, during December 2015. Investigation of this precipitation driven fjord system during a strong El Niño may help us to understand the impacts that warming oceans have on the ability of fjords to act as sinks for atmospheric CO₂. Depth profiles at 12 stations began outside of Nootka Sound and went into the head of Muchalat Inlet. Vertical profiles and water samples at 5 depths were collected using the CTD rosette system onboard the R/V Thomas G. Thompson. Additional samples from the surface 10cm of the water column were collected within 2 of the inner fjords, Muchalat and Tahsis. Analysis of these samples for dissolved inorganic carbon (DIC) and alkalinity allowed for the calculation of pCO₂, a measure of the partial pressure of CO₂ in water. From this and atmospheric pCO₂ data provided by Environment Canada, the flux of CO₂ across the air-sea interface was calculated. Preliminary results of surface samples show effluxes of CO₂ near riverine inputs, while surface waters within the inlets appear to be in near equilibrium with the atmosphere. Preliminary transect results show deep waters have higher pCO₂, further analysis will reveal if a relationship between air-surface fluxes and deep water exists.

Sediment cores were collected from White Lake (15°2.46' S 167°5.35' E) and Red Lake (15°1.97' S 167°5.40' E), located on Thion Island, Vanuatu, to analyze precipitation patterns in the South Pacific Convergence Zone (SPCZ) during the last millennium. The SPCZ is a poorly understood and understudied region of the Tropical Pacific, with a very short instrumental record of rainfall. Extending the record of natural variability in precipitation is important for assessing future risks of freshwater availability to islands in the tropical pacific. Known for high precipitation rates and spanning 3000 km in a NW to SE orientation, the South Pacific Convergence Zone is the most prominent rainfall feature in the Southern Hemisphere. These freshwater lakes contain the dinoflagellate sterol, dinosterol, which acts as a “molecular fossil” or lipid biomarker and is used to infer variations of the deuterium/protium (²H/¹H) isotopic ratio of the lake water over time since algal lipids track changes in environmental water. The fluctuations in the ²H/¹H ratio in both the lake water and dinosterol are linked to changes in SPCZ precipitation since in the tropics, the rainfall rate is correlated with the isotopic composition of rain. Dinosterol was purified using column chromatography and High Performance Liquid Chromatography, identified and then quantified using Gas Chromatography-Mass Spectrometry and Gas Chromatography-Flame Ionization Detection. The ²H/¹H ratio of the purified dinosterol was determined using Gas Chromatography-Isotope Ratio Mass Spectrometry.