the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
A dynamical reconstruction of the Last Glacial Maximum ocean state constrained by global oxygen isotope data
Charlotte Breitkreuz
André Paul
Michael Schulz
Abstract. Combining ocean general circulation models with proxy data via data assimilation is a means to obtain estimates of past ocean states that are consistent with model physics as well as with proxy data. The climate during the Last Glacial Maximum (LGM, 19–23 ka) was substantially different from today. Even though boundary conditions are comparatively well known, the large-scale patterns of the ocean circulation during this time remain uncertain. Previous efforts to combine ocean models with proxy data have shown dissimilar results regarding the state of the ocean, in particular of the Atlantic Meridional Overturning Circulation. Here, we present a new LGM ocean state estimate that extents previous estimates by using global benthic as well as planktic data on the oxygen isotopic composition of calcite. It is further constrained by global seasonal and annual sea surface temperature (SST) reconstructions. The estimate shows an Atlantic Ocean that is similar to the Late Holocene Atlantic Ocean but with a reduced formation of Antarctic Bottom Water, in contrast to results of previous studies. The results indicate that SST and oxygen isotopic data alone do not require the presence of a shallower North Atlantic Deep Water and a more extensive Antarctic Bottom Water, and highlight the need for more proxy data of different types to obtain reliable ocean state estimates. Additional adjoint sensitivity experiments reveal that data from the deep North Atlantic and from the global deep Southern Ocean are most important to constrain the Atlantic Meridional Overturning Circulation.
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Preprint
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Charlotte Breitkreuz et al.
Interactive discussion


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RC1: 'review', Anonymous Referee #1, 30 May 2019
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RC2: 'review', Anonymous Referee #2, 13 Jun 2019
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RC3: 'Review of Breitkreuz et al.', Anonymous Referee #3, 18 Jun 2019
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EC1: 'It is not yet the end of the discussion phase', Marie-France Loutre, 18 Jun 2019
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RC4: 'Interactive comment on “A dynamical reconstruction of the Last Glacial Maximum ocean state constrained by global oxygen isotope data” by Charlotte Breitkreuz et al.', Anonymous Referee #4, 24 Jun 2019
Interactive discussion


-
RC1: 'review', Anonymous Referee #1, 30 May 2019
-
RC2: 'review', Anonymous Referee #2, 13 Jun 2019
-
RC3: 'Review of Breitkreuz et al.', Anonymous Referee #3, 18 Jun 2019
-
EC1: 'It is not yet the end of the discussion phase', Marie-France Loutre, 18 Jun 2019
-
RC4: 'Interactive comment on “A dynamical reconstruction of the Last Glacial Maximum ocean state constrained by global oxygen isotope data” by Charlotte Breitkreuz et al.', Anonymous Referee #4, 24 Jun 2019
Charlotte Breitkreuz et al.
Charlotte Breitkreuz et al.
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