Foraminifera Trace Anthropogenic CO₂ in the NW Atlantic by 1950

Abstract

The Northwest Atlantic is a region of major climate change over the twentieth century, affected by the weakening of the Atlantic meridional overturning circulation. To assess whether the ability of this region to absorb anthropogenic CO 2 has been impacted by this change, we present the region's first long-term carbon isotope (δ 13 C) time series of fossil foraminifera spanning the past 4,000 years. These records reveal an unprecedented negative δ 13 C excursion driven by anthropogenic CO 2 penetration into the surface ocean, the "Suess effect" signal. This signal (amplitude −0.45‰) emerges in 1950 CE ± 15 with a decrease rate of 0.009 ± 0.001‰/yr. This marine signal is~30% of the atmospheric Suess effect and emerges over a century later. Based on current estimates of the ratio of δ 13 C DIC change to dissolved inorganic carbon change and limited constraints on surface ocean residence times, we calculate a mean anthropogenic CO 2 uptake rate of 0.6 ± 0.2 μmol/(kg yr) from 1950 to 2005. Plain Language SummarySince the industrial revolution, the burning of fossil fuels for human energy and transportation needs has caused an accumulation of carbon dioxide (CO 2 ) in the atmosphere. Over the same time period, nearly 30% of CO 2 emissions have been taken up by the ocean. This absorption is not uniform; therefore, understanding local CO 2 uptake rates is essential for assessing future ocean acidification risk. Our study investigates and presents the first long-term history of carbon for the Northwest Atlantic shelf region. The CO 2 emitted from fossil fuel burning has a distinct carbon isotope ratio compared to the preindustrial background level. Organisms called foraminifera incorporate the carbon isotope ratio of ocean carbon into their shells, which eventually sink to the seafloor where they are preserved in the sediments. For our analysis, we collected five sediment cores containing foraminifera from the NW Atlantic, resulting in carbon isotope records that span the last 4,000 years. We find evidence of fossil fuel-derived CO 2 in the NW Atlantic starting in 1950 and translate carbon isotope trends into estimates of fossil fuel CO 2 uptake rates by the surface ocean. Results from our study can be used to assess and predict future ocean acidification risk.

Sedimentary Anthropogenic Carbon Signals From the Western Pacific Margin for the Last Century

“…The 13 C-depleted carbon has been widely reported in coral skeleton and sclerosponge (Druffel and Benavides, 1986;Swart et al, 1996a;Swart et al, 1996b;Swart et al, 2010;Al-Rousan and Felis, 2013;Hou et al, 2019;Liu et al, 2021) and planktonic foraminifera (Al-Rousan et al, 2004;Black et al, 2011;Xu et al, 2014;Mellon et al, The light gray symbol shows all the δ 13 C of planktonic foraminifers in this study, and the LOESS fit represent the situation in the mid-low latitude Pacific Ocean. The orange, purple, and light blue lines represent the situation of planktonic foraminifera in the Atlantic Ocean at low, mid, and high latitudes, respectively (adopted from Black et al, 2011;Mellon et al, 2019;Simon et al, 2020). The δ 13 C axis of these three data sets was shifted to facilitate comparison with our data.…”

“…Although there were isotopic offsets between precipitated calcium carbonate shells and the ambient seawater, Mellon et al (2019) have indicated that decline trends of the δ 13 C recorded by different species of foraminiferal were still consistent. To compare δ 13 C among different planktonic foraminiferal records, data published in previous studies were digitalized and plotted with the long-term variability of measured planktonic δ 13 C in this study (Figure 4E).…”

“…The decline trend of δ 13 C in the surface ocean was caused by the input of radiocarbon-dead or anthropogenic-produced 13 C-depleted carbons from the atmosphere through the air-sea exchange process (Suess, 1955;Keeling, 1979;Broecker and Maier-Reimer, 1992;Quay et al, 1992). The 13 C-depleted carbon has been widely reported in coral skeleton and sclerosponge (Druffel and Benavides, 1986;Swart et al, 1996a;Swart et al, 1996b;Swart et al, 2010;Al-Rousan and Felis, 2013;Hou et al, 2019;Liu et al, 2021) and planktonic foraminifera (Al-Rousan et al, 2004;Black et al, 2011;Xu et al, 2014;Mellon et al, The light gray symbol shows all the δ 13 C of planktonic foraminifers in this study, and the LOESS fit represent the situation in the mid-low latitude Pacific Ocean. The orange, purple, and light blue lines represent the situation of planktonic foraminifera in the Atlantic Ocean at low, mid, and high latitudes, respectively (adopted from Black et al, 2011;Mellon et al, 2019;Simon et al, 2020).…”

“…The 13 C Suess effect is not only archived in the atmosphere (Suess, 1955;Friedli et al, 1986) but also imprinted in marine realms (Quay et al, 1992;Swart et al, 2010;Black et al, 2011;Mellon et al, 2019;Simon et al, 2020). The significant decline trend of the δ 13 C was measured in corals or sclerosponges pervasively distributed over the Atlantic, Indian, and Pacific Oceans (Damon et al, 1978;Nozaki et al, 1978;Druffel and Benavides, 1986;Wei et al, 2009;Swart et al, 2010).…”

“…The foraminiferal δ 13 C records are often used to extract the environmental and metabolic information, though the offset exists because of physical and biogeological processes (Spero and Williams, 1988;Jonkers et al, 2013;Gaskell and Hull, 2019). For example, the fossil benthic foraminifera had indicated the negative excursion of the long-term δ 13 C variability occurring within this century, which was related to the anthropogenic CO 2 emission (Al-Rousan et al, 2004;Mellon et al, 2019).…”