Ocean warming, acidification, and chemistry of the South Pacific & North Atlantic: a brachiopod investigation

Abstract

Global CO2 emissions drive ocean warming and acidification. Local-level ocean data is limited, so natural archives like brachiopods are used to understand past oceanic conditions. Brachiopod shells record seawater temperatures, chemistry, and acidity. This thesis uses brachiopods from Paterson Inlet, New Zealand (1900–2021), and the Bay of Fundy, Canada (1970–2009) to track past oceanographic conditions and fill local data gaps. Global oceans recorded a decrease in δ13C DIC values of 0.50 ‰ (~1900-1985), comparable to the δ13CB value of -0.48‰ for Paterson Inlet (1900-2014), a rate of -0.04‰ per decade. The Bay of Fundy brachiopods recorded decreasing δ13CB values by 0.25‰ per decade (1970-2009). Ocean acidification is driven by the mixing of atmospheric CO2, and anthropogenic emissions are enriched in 12C, suggesting a link between pH and δ13CB values. The brachiopod shells δ18OB and Li/Ca levels record ambient seawater temperatures. In Paterson Inlet, seawater temperatures calculated with Li/Ca and δ18O values suggest cooling (ΔT = -0.035℃ per decade; 1900-2014). Temperatures calculated with δ18OB values for the Bay of Fundy indicate cooling (-0.25°C per decade; 1970-2009). Bay of Fundy seawater has recorded decreasing δ18OSW values by -0.16 ‰ per decade (1970-2022), reflecting potential arctic meltwater influx, cooling the seawater. The burning of coal drives CO2 emissions. Coal emissions contain various heavy metals, including selenium. Brachiopods record an increase in selenium concentrations of +6.14 mmol (1926-1960). Subsequently, in 1960-1980, selenium content decreased by -7.54 mmol but has since been increasing with a slightly upward trend of +1.78 mmol (2009-2021). Similar trends are observed in the brachiopod’s lanthanum content, another element found in coal, suggesting that brachiopod shell chemistry contains a record of coal burning. Archives such as brachiopods are an important source of information regarding the changing oceans. Although systems exist to monitor oceanic conditions, they cannot trace small-scaled effects. Brachiopods from Paterson Inlet and the Bay of Fundy record local changes in seawater conditions over the past 120 years. Some trends, such as δ13CB values, correspond with global ones, while others, such as temperatures, are not, reflecting the complex interaction of climate and weather/oceanographic changes on a local scale.