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Kawasaki T.,Japan National Institute of Polar Research | Hasumi H.,Atmosphere and Ocean Research Institute
Journal of Geophysical Research: Oceans | Year: 2016

The heat influx of the Atlantic water and its interannual variability through the Fram Strait toward the Arctic Ocean are examined by using a realistically configured ice-ocean general circulation model. The modeled routes of the Atlantic water and high eddy activity around the Fram Strait are consistent with many observations. Two-thirds of the heat transported by the Atlantic water passing through the Fram Strait (78°N) is lost by the westward transport and the sea surface cooling, and the other one-third is injected to the Arctic Ocean. The contribution of oceanic eddy to the westward heat transport is 5% of that of mean current. The variability of sea level pressure anomaly centered at the Nordic Seas explains the interannual variability of the heat passing through the Fram Strait, transported westward, and cooled at the sea surface in the north of the Fram Strait. The interannual variabilities of these heat fluxes have significant correlations with the NAO. The interannual variability of heat transported by the Atlantic water and entering the Arctic Ocean is caused by the variability of the Siberian high. © 2015. American Geophysical Union. All Rights Reserved.

Yokoyama Y.,Atmosphere and Ocean Research Institute | Yokoyama Y.,University of Tokyo | Yokoyama Y.,Japan Agency for Marine - Earth Science and Technology | Yokoyama Y.,Australian Nuclear Science and Technology Organisation | Esat T.M.,Australian National University
Oceanography | Year: 2011

Although climate variations and sea level changes are often discussed interchangeably, climate change need not always result in sea level change. Perturbations in Earth's orbit cause major climate changes, and the resulting variations in the amount and distribution of solar radiation at ground level follow cycles lasting for thousands of years. Research done in the last decade shows that climate can change on centennial or shorter time scales. These more rapid changes appear to be related to modifications in ocean circulation initiated during the last glacial period either by injections of fresh meltwater or huge ice discharges into the North Atlantic. When first detected, these rapid climate changes were characterized as episodes decoupled from any significant change in sea level. New data clearly show a direct connection between climate and sea level, and even more surprising, this link may extend to times of glacial-interglacial transitions and possibly also to interglacials. The full extent of this sea level/climate coupling is unknown and is the subject of current research. © 2011 by The Oceanography Society. All rights reserved.

Hiraike Y.,Atmosphere and Ocean Research Institute | Tanaka Y.,Japan Agency for Marine - Earth Science and Technology | Hasumi H.,Atmosphere and Ocean Research Institute
Journal of Geophysical Research: Oceans | Year: 2016

The subduction process of Pacific Antarctic Intermediate Water (PAAIW) in the Pacific is investigated using output from an eddy-resolving ocean model. Focus is on contribution of eddies to the subduction process. To separate the subduction rate into contributions by eddies and mean flows, the temporal residual mean (TRM) velocity is used. In the mean subduction rate, lateral induction caused by the strong eastward flow of the Antarctic Circumpolar Current (ACC) is dominant. The largest rate is located in the Drake Passage. The estimated eddy-induced subduction rate is comparable with the mean subduction rate, and it tends to cancel the vertical mean component in many regions. In the west of the Drake Passage, however, the eddy-induced subduction is larger than the vertical mean component, and this eddy-induced subduction was not detected in previous studies using the thickness diffusion parameterization and an eddy-permitting model. Results of idealized sensitivity studies to model resolution suggest that the subduction rate would be larger using a model with higher vertical resolution. © 2015. American Geophysical Union.

Tanaka Y.,Atmosphere and Ocean Research Institute | Tanaka Y.,University of Tokyo | Yasuda I.,Atmosphere and Ocean Research Institute | Hasumi H.,Atmosphere and Ocean Research Institute | And 3 more authors.
Journal of Climate | Year: 2012

Diapycnal mixing induced by tide-topography interaction, one of the essential factors maintaining the global ocean circulation and hence the global climate, is modulated by the 18.6-yr period oscillation of the lunar orbital inclination, and has therefore been hypothesized to influence bidecadal climate variability. In thisstudy, the spatial distribution of diapycnal diffusivity together with its 18.6-yr oscillation estimated from a global tide model is incorporated into a state-of-the-art numerical coupled climatemodel to investigate its effects on climate variability over the North Pacific and to understand the underlying physical mechanism. It is shown that a significant sea surface temperature (SST) anomaly with a period of 18.6 years appears in the Kuroshio-Oyashio Extension region; a positive (negative)SST anomaly tends to occur during strong (weak) tidal mixing. This is first induced by anomalous horizontal circulation localized around the Kuril Straits, where enhanced modulation of tidal mixing exists, and then amplified through a positive feedback due to midlatitude air-sea interactions. The resulting SST and sea level pressure variability patterns are reminiscent of those associated with one of the most prominent modes of climate variability in the North Pacific known as the Pacific decadal oscillation, suggesting the potential for improving climate predictability by taking into account the 18.6-yr modulation of tidal mixing. © 2012 American Meteorological Society.

Thomas A.L.,University of Oxford | Fujita K.,University of Ryukyus | Iryu Y.,Tohoku University | Iryu Y.,Nagoya University | And 29 more authors.
Marine Geology | Year: 2012

We present uranium-thorium chronology for a 102m core through a Pleistocene reef at Tahiti (French Polynesia) sampled during IODP Expedition 310 "Tahiti Sea Level". We employ total and partial dissolution procedures on the older coral samples to investigate the diagenetic overprint of the uranium-thorium system. Although alteration of the U-Th system cannot be robustly corrected, diagenetic trends in the U-Th data, combined with sea level and subsidence constraints for the growth of the corals enables the age of critical samples to be constrained to marine isotope stage 9. We use the ages of the corals, together with δ 18O based sea-level histories, to provide maximum constraints on possible paleo water-depths. These depth constraints are then compared to independent depth estimates based on algal and foraminiferal assemblages, microbioerosion patterns, and sedimentary facies, confirming the accuracy of these paleo water-depth estimates. We also use the fact that corals could not have grown above sea level to place a maximum constraint on the subsidence rate of Tahiti to be 0.39mka -1, with the most likely rate being close to the existing minimum estimate of 0.25mka -1. © 2011 Elsevier B.V.

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