A synthesis of marine sediment core δ<sup>13</sup>C data over the last 150 000 years

Abstract

The isotopic composition of carbon, &delta;¹³C, in seawater is used in reconstructions of ocean circulation, marine productivity, air-sea gas exchange, and biosphere carbon storage. Here, a synthesis of &delta;¹³C measurements taken from foraminifera in marine sediment cores over the last 150 000 years is presented. The dataset comprises previously published and unpublished data from benthic and planktonic records throughout the global ocean. Data are placed on a common &delta;¹⁸O age scale suitable for examining orbital timescale variability but not millennial events, which are removed by a 10 ka filter. Error estimates account for the resolution and scatter of the original data, and uncertainty in the relationship between &delta;¹³C of calcite and of dissolved inorganic carbon (DIC) in seawater. This will assist comparison with &delta;¹³C of DIC output from models, which can be further improved using model outputs such as temperature, DIC concentration, and alkalinity to improve estimates of fractionation during calcite formation. <br><br> High global deep ocean &delta;¹³C, indicating isotopically heavy carbon, is obtained during Marine Isotope Stages (MIS) 1, 3, 5a, c and e, and low &delta;¹³C during MIS 2, 4 and 6, which are temperature minima, with larger amplitude variability in the Atlantic Ocean than the Pacific Ocean. This is likely to result from changes in biosphere carbon storage, modulated by changes in ocean circulation, productivity, and air-sea gas exchange. The North Atlantic vertical &delta;¹³C gradient is greater during temperature minima than temperature maxima, attributed to changes in the spatial extent of Atlantic source waters. There are insufficient data from shallower than 2500 m to obtain a coherent pattern in other ocean basins. The data synthesis indicates that basin-scale &delta;¹³C during the last interglacial (MIS 5e) is not clearly distinguishable from the Holocene (MIS 1) or from MIS 5a and 5c, despite significant differences in ice volume and atmospheric CO₂ concentration during these intervals. Similarly, MIS 6 is only distinguishable from MIS 2 or 4 due to globally lower &delta;¹³C values both in benthic and planktonic data. This result is obtained despite individual records showing differences between these intervals, indicating that care must be used in interpreting large scale signals from a small number of records

Mode change of millennial CO 2 variability during the last glacial cycle associated with a bipolar marine carbon seesaw

“…The salient difference from MIS 5 to MIS 3 conditions therefore appears to be the presence of a weakly ventilated, carbon-rich water mass in the deep Atlantic Ocean. This is supported by a synthesis of benthic δ 13 C records (31), which shows a decrease of δ 13 C in the Atlantic basin and the Southern Ocean at the MIS 5-4 transition (Fig. 3E).…”

A reconstruction of atmospheric carbon dioxide and its stable carbon isotopic composition from the penultimate glacial maximum to the last glacial inception

“…Increasing carbonate ion concentration in the deep ocean due to ocean reorganization within a glacial termination may have triggered a deepening of the carbonate compensation depth by about 700 m (Farrel and Prell, 1989;Broecker et al, 1993), which allows for enhanced CaCO 3 preservation in the Atlantic and the Pacific Oceans. A strengthening of deep ocean ventilation during the termination is also supported by deep sea δ 13 C reconstructions of benthic sediment cores (Oliver et al, 2010). Those show increasing deep ocean δ 13 C values throughout the LGM and Termination I, indicating a decrease of the δ 13 C surface to deep ocean gradient (Hodell et al, 2003).…”

“…In fact the preservation records (Atlantic and Pacific) are already half way up from their minimum values when the deglaciation starts, pointing to internal processes of the alkalinity budget of the ocean rather than circulation to be responsible for this long-term trend in the preservation history. Note also that the preservation state in the deep ocean was already on a higher level during the PGM than for the LGM, while at the end of Termination II the magnitude of preservation was the same as after Termination I. Additionally, deep ocean δ 13 C DIC (Oliver et al, 2010) started to rise at least 10 000 yr before the PGM, while δ 13 C DIC in the deep ocean decreased for 10 000 yr before the LGM. As shown by transient simulations over the past 130 000 yr with a 3-D dynamic ocean model, a multitude of physical and biogeochemical processes influences the spatio-temporal evolution of carbonate preservation, δ 13 C of dissolved inorganic carbon, atmospheric CO 2 , δ 13 C atm , and other proxies on millennial and even longer timescales.…”

Modelling δ13C in benthic foraminifera: Insights from model sensitivity experiments

“…These could then be compared to observational data from sediment cores (e.g. Oliver et al (2010)), comparable to the approach of Hesse et al (2011), and allow for a more nuanced interpretation of possible glacial implications of our findings.…”