Last Glacial Maximum and deglacial abyssal seawater oxygen isotopic ratios

Abstract

Abstract. An earlier analysis of pore-water salinity (chlorinity) in two deep-sea cores, using terminal constraint methods of control theory, concluded that although a salinity amplification in the abyss was possible during the LGM, it was not required by the data. Here the same methodology is applied to δ 18 O w in the upper 100 m of four deep-sea cores. An ice volume amplification to the isotopic ratio is, again, consistent with the data but not required by it. In particular, results are very sensitive, with conventional diffusion values, to the assumed initial conditions at −100 ky and a long list of noise (uncertainty) assumptions. If the calcite values of δ 18 O are fully reliable, then published enriched values of the ratio in seawater are necessary to preclude sub-freezing temperatures, but the seawater δ 18 O in pore fluids does not independently require the conclusion.

Dynamical reconstruction of the global ocean state during the Last Glacial Maximum

“…The reconstructed LGM δ 18 O water could be directly compared with the oxygen‐isotope composition of seawater restored from pore water samples from seafloor sediments [ Adkins et al , ], although the δ 18 O water may not be determined uniquely from the pore water [ Wunsch , ]. Our result for the Southern Hemisphere (Ocean Drilling Program (ODP) site 1093) agrees with the pore water value within the errors, whereas our estimates for the Northern Hemisphere were considerably higher than the observations (Table ).…”

“…On the other hand, the reconstructed ocean state in LGM400 was more stratified in salinity and density (Figure ). Several lines of independent evidence support this result [ Adkins et al , ; Insua et al , ], although a recent study suggests that salinity amplification in the abyss during the LGM is not necessarily constrained by the data [ Wunsch , ]. A more stratified ocean would be consistent with a larger carbon storage in the deep ocean, which would contribute to a lower p CO 2 in the atmosphere [e.g., Sigman and Boyle , ; Marchitto et al , ], in particular in conjunction with a larger volume of Antarctic Bottom Water (AABW) as shown in Brovkin et al [].…”

Simulation of climate, ice sheets and CO<sub>2</sub> evolution during the last four glacial cycles with an Earth system model of intermediate complexity

“…Such an increase in salinity is indeed difficult to reproduce without contribution of brines. However, the accuracy of salinity reconstructions based on such a method remains uncertain (Wunsch, 2016). Second, there is a problem with the temporal dynamics of brine rejection ef-ficiency.…”

Testing Methods for Reconstructing Glacial Antarctic Circumpolar Current Transport in an Isotope‐Enabled Climate Model

“…The uncertainties in the temperature and salinity of LCDW are taken from Adkins et al (2002). There are suggestions that the errors on the pore water reconstruction may be underestimated (Miller et al, 2015;Wunsch, 2016aWunsch, , 2016b. These uncertainties and its implications may in turn result in larger transport error and need to be considered in a real-world paleo-application.…”