M. O. Chikamoto

The University of Texas at Austin

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Ayako Abe‐Ouchi

The University of Tokyo

Axel Timmermann

Pusan National University

Rumi Ohgaito

Japan Agency for Marine-Earth Science and Technology

Laurie Menviel

UNSW Sydney

Akira Oka

Howard University

Masakazu Yoshimori

The University of Tokyo

Naomi Harada

Japan Agency for Marine-Earth Science and Technology

Michael E Weber

University of Bonn

Yusuke Okazaki

Tokyo University of Science

Daniela Sprenk

University of Cologne

Cooperative Institutions

Japan Agency for Marine-Earth Science and Technology

The University of Tokyo

University of Hawaii System

Max Planck Institute for Meteorology

University of Hawaiʻi at Mānoa

Hokkaido University

Centre National de la Recherche Scientifique

Pacific International Center for High Technology Research

Sphere Institute

National Institute of Polar Research

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Response of deep‐sea CaCO₃ sedimentation to Atlantic meridional overturning circulation shutdown

Journal of Geophysical Research Atmospheres (2008)

M. O. Chikamoto Katsumi Matsumoto Andy Ridgwell

Changes in the distribution of the preservation and burial of calcium carbonate (CaCO 3 ) in deep ocean sediments and associated atmospheric p CO 2 response to the shutdown of the Atlantic meridional overturning circulation (MOC) are examined using an Earth system model. We find that shutdown of the Atlantic MOC forced by the freshwater inflow significantly decreases the CaCO 3 content in North Atlantic sediments. This is a consequence of a decrease in bottom‐water carbonate ion concentrations and reduction in sea‐surface CaCO 3 production. The main sedimentary impacts of these two effects are separated in time, however, with reduced CaCO 3 production dominating the decrease in CaCO 3 burial during the first 1000 years after the forcing is applied. In the absence of significant overturning circulation in the Atlantic, atmospheric p CO 2 increases by 11 ppm, largely due to a decrease in POC export and a weakening biological pump. The change in p CO 2 induced by reorganization of CaCO 3 burial in deep‐sea sediments is small, only 1 ppm, because increased preservation of CaCO 3 in the Pacific largely efficiently buffers decreased preservation in the Atlantic, leaving the global burial and ocean alkalinity minimally changed at equilibrium.

Alkalinity

Sedimentation

Biological pump

Tropical Atlantic

10.1029/2007jg000669

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Glacial marine carbon cycle sensitivities to Atlantic ocean circulation reorganization by coupled climate model simulations

M. O. Chikamoto Ayako Abe‐Ouchi Akira Oka Rumi Ohgaito Axel Timmermann

Abstract. A series of Last Glacial Maximum (LGM) marine carbon cycle sensitivity experiments is conducted to test the effect of different physical processes, as simulated by two atmosphere-ocean general circulation model (AOGCM) experiments, on the atmospheric pCO2. One AOGCM solution exhibits an increase in North Atlantic Deep Water (NADW) formation, whereas the other mimics an increase in Antarctic Bottom Water (AABW) associated with a weaker NADW. Due to enhanced gas solubility associated with lower sea surface temperature, both experiments generate a reduction of atmospheric pCO2 by about 20–23 ppm. However, neither a weakening of NADW nor an increase of AABW formation causes a large atmospheric pCO2 change. A marked enhancement in AABW formation is required to represent the reconstructed vertical gradient of dissolved inorganic carbon (DIC) during LGM conditions. The efficiency of Southern Ocean nutrient utilization reduces in response to an enhanced AABW formation, which counteracts the circulation-induced ocean carbon uptake.

Last Glacial Maximum

Antarctic Bottom Water

10.5194/cpd-7-1261-2011

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Glacial Atlantic Overturning in CMIP/PMIP models controlled by the Southern and Northern high latitude changes

Ayako Abe‐Ouchi Rumi Ohgaito K. Takahashi M. O. Chikamoto Sam Sherriff‐Tadano

High latitude

Last Glacial Maximum

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The North Pacific's role in Pleistocene climate

AGU Fall Meeting Abstracts (2011)

Axel Timmermann Yusuke Okazaki Naomi Harada Laurie Menviel M. O. Chikamoto

Source

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Interaction between ocean circulation and sea-ice coverage controlling marine carbon cycle

EGU General Assembly Conference Abstracts (2010)

M. O. Chikamoto Ayako Abe‐Ouchi Akira Oka Rumi Ohgaito

Circulation (fluid dynamics)

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Mechanisms and predictability of multiyear ecosystem variability in the North Pacific

Global Biogeochemical Cycles (2015)

M. O. Chikamoto Axel Timmermann Yoshimitsu Chikamoto Hiroki Tokinaga Naomi Harada

Abstract Aleutian Low variations provide vorticity, buoyancy, and heat‐flux forcing to the North Pacific Ocean, which in turn cause changes in ocean circulation, mixed layer characteristics and sea ice coverage. In this process the white noise atmospheric characteristics are integrated dynamically and thermodynamically to generate red noise ocean spectra. Using the Community Earth System Model (version 1.0.3) we study the resulting biogeochemical and ecosystem responses in the North Pacific. We find that ocean dynamical variables have an impact on the tendencies of key nutrients and biological production, which leads to a further reddening of biogeochemical spectra resulting in potential predictability on time scales of 2–4 years. However, this low‐pass filtering does not apply to all biogeochemical variables and is regionally dependent. It is shown that phytoplankton biomass in the Central North Pacific adjusts to the much shorter‐term variability associated with changes in mixed layer depth, light availability, and zooplankton grazing, thus limiting the predictability of phytoplankton anomalies to about 1 year. In the eastern North Pacific the slow advection of anomalous nutrient concentrations leads to longer persistence of phytoplankton variability and increased potential predictability of up to 3 years.

Biogeochemical Cycle

Predictability

Biogeochemistry

Forcing (mathematics)

Mixed layer

10.1002/2015gb005096

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Iceberg-rafted debris from sediment core MD07-3133

Michael E Weber Peter U. Clark Gerhard Kühn Axel Timmermann Daniela Sprenk

Sediment core

Iceberg