Decadal to multidecadal variability of the Atlantic MOC: Mechanisms and predictability

Abstract. Several proxy-based and modeling studies have investigated long-term changes in Caribbean climate during the Holocene, however, very little is known on its variability on short timescales. Here we reconstruct seasonality and interannual to multidecadal variability of sea surface hydrology of the southern Caribbean Sea by applying paired coral Sr/Ca and δ18O measurements on fossil annually banded Diploria strigosa corals from Bonaire. This allows for better understanding of seasonal to multidecadal variability of the Caribbean hydrological cycle during the mid- to late Holocene. The monthly resolved coral Δδ18O records are used as a proxy for the oxygen isotopic composition of seawater (δ18Osw) of the southern Caribbean Sea. Consistent with modern day conditions, annual δ18Osw cycles reconstructed from three modern corals reveal that freshwater budget at the study site is influenced by both net precipitation and advection of tropical freshwater brought by wind-driven surface currents. In contrast, the annual δ18Osw cycle reconstructed from a mid-Holocene coral indicates a sharp peak towards more negative values in summer, suggesting intense summer precipitation at 6 ka BP (before present). In line with this, our model simulations indicate that increased seasonality of the hydrological cycle at 6 ka BP results from enhanced precipitation in summertime. On interannual to multidecadal timescales, the systematic positive correlation observed between reconstructed sea surface temperature and salinity suggests that freshwater discharged from the Orinoco and Amazon rivers and transported into the Caribbean by wind-driven surface currents is a critical component influencing sea surface hydrology on these timescales.

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On the enhancement of the Indian summer monsoon drying by Pacific multidecadal variability during the latter half of the twentieth century

Journal of Geophysical Research Atmospheres ◽

10.1002/2015jd023313 ◽

2015 ◽

Vol 120 (18) ◽

pp. 9103-9118 ◽

Cited By ~ 8

Author(s):

M. Salzmann ◽

R. Cherian

Keyword(s):

Twentieth Century ◽

Summer Monsoon ◽

Indian Summer Monsoon ◽

Multidecadal Variability

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The amplitude of decadal to multidecadal variability in precipitation simulated by state-of-the-art climate models

Geophysical Research Letters ◽

10.1029/2012gl053424 ◽

2012 ◽

Vol 39 (21) ◽

pp. n/a-n/a ◽

Cited By ~ 45

Author(s):

T. R. Ault ◽

J. E. Cole ◽

S. St. George

Keyword(s):

Climate Models ◽

State Of The Art ◽

Multidecadal Variability

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Arctic–North Atlantic Interactions and Multidecadal Variability of the Meridional Overturning Circulation

Journal of Climate ◽

10.1175/jcli3462.1 ◽

2005 ◽

Vol 18 (19) ◽

pp. 4013-4031 ◽

Cited By ~ 190

Author(s):

Johann H. Jungclaus ◽

Helmuth Haak ◽

Mojib Latif ◽

Uwe Mikolajewicz

Keyword(s):

North Atlantic ◽

Deep Water ◽

Ocean Model ◽

Meridional Overturning Circulation ◽

The Arctic ◽

Deep Water Formation ◽

Overturning Circulation ◽

Multidecadal Variability ◽

Water Formation ◽

Meridional Overturning

Abstract Analyses of a 500-yr control integration with the non-flux-adjusted coupled atmosphere–sea ice–ocean model ECHAM5/Max-Planck-Institute Ocean Model (MPI-OM) show pronounced multidecadal fluctuations of the Atlantic overturning circulation and the associated meridional heat transport. The period of the oscillations is about 70–80 yr. The low-frequency variability of the meridional overturning circulation (MOC) contributes substantially to sea surface temperature and sea ice fluctuations in the North Atlantic. The strength of the overturning circulation is related to the convective activity in the deep-water formation regions, most notably the Labrador Sea, and the time-varying control on the freshwater export from the Arctic to the convection sites modulates the overturning circulation. The variability is sustained by an interplay between the storage and release of freshwater from the central Arctic and circulation changes in the Nordic Seas that are caused by variations in the Atlantic heat and salt transport. The relatively high resolution in the deep-water formation region and the Arctic Ocean suggests that a better representation of convective and frontal processes not only leads to an improvement in the mean state but also introduces new mechanisms determining multidecadal variability in large-scale ocean circulation.

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Decadal to Multidecadal Variability of the Mixed Layer to the South of the Kuroshio Extension Region

Journal of Climate ◽

10.1175/jcli-d-20-0115.1 ◽

2020 ◽

Vol 33 (17) ◽

pp. 7697-7714

Author(s):

Baolan Wu ◽

Xiaopei Lin ◽

Lisan Yu

Keyword(s):

Heat Flux ◽

Pacific Ocean ◽

Mixed Layer ◽

Kuroshio Extension ◽

Mixed Layer Depth ◽

Layer Depth ◽

Multidecadal Variability ◽

Mixed Layer Temperature ◽

The Kuroshio ◽

The Western Pacific

AbstractThe decadal to multidecadal mixed layer variability is investigated in a region south of the Kuroshio Extension (130°E–180°, 25°–35°N), an area where the North Pacific subtropical mode water forms, during 1948–2012. By analyzing the mixed layer heat budget with different observational and reanalysis data, here we show that the decadal to multidecadal variability of the mixed layer temperature and mixed layer depth is covaried with the Atlantic multidecadal oscillation (AMO), instead of the Pacific decadal oscillation (PDO). The mixed layer temperature has strong decadal to multidecadal variability, being warm before 1970 and after 1990 (AMO positive phase) and cold during 1970–90 (AMO negative phase), and so does the mixed layer depth. The dominant process for the mixed layer temperature decadal to multidecadal variability is the Ekman advection, which is controlled by the zonal wind changes related to the AMO. The net heat flux into the ocean surface Qnet acts as a damping term and it is mainly from the effect of latent heat flux and partially from sensible heat flux. While the wind as well as mixed layer temperature decadal changes related to the PDO are weak in the western Pacific Ocean. Our finding proposes the possible influence of the AMO on the northwestern Pacific Ocean mixed layer variability, and could be a potential predictor for the decadal to multidecadal climate variability in the western Pacific Ocean.

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