scholarly journals Tropical North Atlantic subsurface warming events as a fingerprint for AMOC variability during Marine Isotope Stage 3

2015 ◽  
Vol 30 (11) ◽  
pp. 1425-1436 ◽  
Author(s):  
Andrew O. Parker ◽  
Matthew W. Schmidt ◽  
Ping Chang
Keyword(s):  
North Atlantic ◽  
Marine Isotope Stage ◽  
Tropical North Atlantic ◽  
Marine Isotope Stage 3

scholarly journals Changes in North Atlantic Deep Water strength and bottom water masses during Marine Isotope Stage 3 (45–35kaBP)

2010 ◽  
Vol 29 (19-20) ◽  
pp. 2451-2461 ◽  
Author(s):  
Marcus Gutjahr ◽  
Babette A.A. Hoogakker ◽  
Martin Frank ◽  
I. Nicholas McCave
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Bottom Water ◽  
North Atlantic Deep Water ◽  
Water Masses ◽  
Marine Isotope Stage ◽  
Marine Isotope Stage 3

scholarly journals A coupled climate model simulation of Marine Isotope Stage 3 stadial climate

2011 ◽  
Vol 7 (1) ◽  
pp. 79-118
Author(s):  
J. Brandefelt ◽  
E. Kjellström ◽  
J.-O. Näslund ◽  
G. Strandberg ◽  
A. H. L. Voelker ◽  
...  
Keyword(s):  
Surface Temperature ◽  
North Atlantic ◽  
Climate Model ◽  
Meridional Overturning Circulation ◽  
Marine Isotope Stage ◽  
Mis 3 ◽  
Enso Teleconnections ◽  
Last 300 Years ◽  
Marine Isotope Stage 3 ◽  
Global Mean

Abstract. We present a coupled global climate model (CGCM) simulation, integrated for 1500 years to quasi-equilibrium, of a stadial (cold period) within Marine Isotope Stage 3 (MIS 3). The simulated Greenland stadial 12 (GS12; ~44 ka BP) annual global mean surface temperature (Ts) is 5.5 °C higher than in the simulated recent past (RP) climate and 1.3 °C lower than in the simulated Last Glacial Maximum (LGM; 21 ka BP) climate. The simulated GS12 climate is evaluated against proxy data of sea surface temperature (SST). Simulated SSTs fall within the uncertainty range of the proxy SSTs for 30–50% of the sites depending on season. Proxy SSTs are higher than simulated SSTs in the Central North Atlantic, in contrast to earlier simulations of MIS 3 stadial climate in which proxy SSTs were found to be lower than simulated SST. The annual global mean Ts only changes by 0.10 °C from model years 500–599 to the last century of the simulation, indicating that the climate system may be close to equilibrium already after 500 years of integration. However, significant regional differences between the last century of the simulation and model years 500–599, with a maximum of 8 °C in temperature and 65% in precipitation in Southeastern Greenland in boreal winter, exist. Further, the agreement between simulated and proxy SST is improved from model years 500–599 to the last century of the simulation. El-Niño-Southern Oscillation (ENSO) teleconnections in mean sea level pressure (MSLP) are analysed for the last 300 years of the GS12, LGM and RP climate simulations. In agreement with an earlier study, we find that GS12 and LGM forcing and boundary conditions induce major modifications to ENSO teleconnections. However, significant differences in the teleconnection patterns are found between a 300-year time-slice starting after 195 model years and the last 300 years of the simulation. Thus we conclude that both the mean state and the variability of the simulated GS12 climate is dependent on the equilibration. The Atlantic Meridional Overturning Circulation (AMOC) slows down by 50% in the GS12 climate as compared to the RP climate. This slowdown is attained without freshwater forcing in the North Atlantic region, a method used in other studies to force an AMOC shutdown. The results presented here suggest that stadial climate, rather that interstadial climate, should be interpreted as a near-equilibrium MIS 3 climate, in contradiction to an earlier modelling study.

scholarly journals A coupled climate model simulation of Marine Isotope Stage 3 stadial climate

2011 ◽  
Vol 7 (2) ◽  
pp. 649-670 ◽  
Author(s):  
J. Brandefelt ◽  
E. Kjellström ◽  
J.-O. Näslund ◽  
G. Strandberg ◽  
A. H. L. Voelker ◽  
...  
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Southern Oscillation ◽  
Global Climate Model ◽  
Meridional Overturning Circulation ◽  
Marine Isotope Stage ◽  
Quasi Equilibrium ◽  
Mis 3 ◽  
Marine Isotope Stage 3 ◽  
Global Mean

Abstract. We present a coupled global climate model (CGCM) simulation, integrated for 1500 yr to quasi-equilibrium, of a stadial (cold period) within Marine Isotope Stage 3 (MIS 3). The simulated Greenland stadial 12 (GS12; ~44 ka BP) annual global mean surface temperature (Ts) is 5.5 °C lower than in the simulated recent past (RP) climate and 1.3 °C higher than in the simulated Last Glacial Maximum (LGM; 21 ka BP) climate. The simulated GS12 is evaluated against proxy data and previous modelling studies of MIS3 stadial climate. We show that the simulated MIS 3 climate, and hence conclusions drawn regarding the dynamics of this climate, is highly model-dependent. The main findings are: (i) Proxy sea surface temperatures (SSTs) are higher than simulated SSTs in the central North Atlantic, in contrast to earlier simulations of MIS 3 stadial climate in which proxy SSTs were found to be lower than simulated SST. (ii) The Atlantic Meridional Overturning Circulation (AMOC) slows down by 50 % in the GS12 climate as compared to the RP climate. This slowdown is attained without freshwater forcing in the North Atlantic region, a method used in other studies to force an AMOC shutdown. (iii) El-Niño-Southern Oscillation (ENSO) teleconnections in mean sea level pressure (MSLP) are significantly modified by GS12 and LGM forcing and boundary conditions. (iv) Both the mean state and variability of the simulated GS12 is dependent on the equilibration. The annual global mean Ts only changes by 0.10 °C from model years 500–599 to the last century of the simulation, indicating that the climate system may be close to equilibrium already after 500 yr of integration. However, significant regional differences between the last century of the simulation and model years 500–599 exist. Further, the difference between simulated and proxy SST is reduced from model years 500–599 to the last century of the simulation. The results of the ENSO variability analysis is also shown to depend on the equilibration.

scholarly journals Particle export fluxes to the oxygen minimum zone of the eastern tropical North Atlantic

2017 ◽  
Vol 14 (7) ◽  
pp. 1825-1838 ◽  
Author(s):  
Anja Engel ◽  
Hannes Wagner ◽  
Frédéric A. C. Le Moigne ◽  
Samuel T. Wilson
Keyword(s):  
Organic Matter ◽  
North Atlantic ◽  
Organic Phosphorus ◽  
Euphotic Zone ◽  
Carbon Export ◽  
Organic Matter Quality ◽  
B Values ◽  
Chl A ◽  
Tropical North Atlantic ◽  
Particle Export

Abstract. In the ocean, sinking of particulate organic matter (POM) drives carbon export from the euphotic zone and supplies nutrition to mesopelagic communities, the feeding and degradation activities of which in turn lead to export flux attenuation. Oxygen (O2) minimum zones (OMZs) with suboxic water layers (< 5 µmol O2 kg−1) show a lower carbon flux attenuation compared to well-oxygenated waters (> 100 µmol O2 kg−1), supposedly due to reduced heterotrophic activity. This study focuses on sinking particle fluxes through hypoxic mesopelagic waters (< 60 µmol O2 kg−1); these represent  ∼  100 times more ocean volume globally compared to suboxic waters, but they have less been studied. Particle export fluxes and attenuation coefficients were determined in the eastern tropical North Atlantic (ETNA) using two surface-tethered drifting sediment trap arrays with seven trapping depths located between 100 and 600 m. Data on particulate matter fluxes were fitted to the normalized power function Fz =  F100 (z∕100)−b, with F100 being the flux at a depth (z) of 100 m and b being the attenuation coefficient. Higher b values suggest stronger flux attenuation and are influenced by factors such as faster degradation at higher temperatures. In this study, b values of organic carbon fluxes varied between 0.74 and 0.80 and were in the intermediate range of previous reports, but lower than expected from seawater temperatures within the upper 500 m. During this study, highest b values were determined for fluxes of particulate hydrolyzable amino acids (PHAA), followed by particulate organic phosphorus (POP), nitrogen (PN), carbon (POC), chlorophyll a (Chl a) and transparent exopolymer particles (TEP), pointing to a sequential degradation of organic matter components during sinking. Our study suggests that in addition to O2 concentration, organic matter composition co-determines transfer efficiency through the mesopelagic. The magnitude of future carbon export fluxes may therefore also depend on how organic matter quality in the surface ocean changes under influence of warming, acidification and enhanced stratification.

scholarly journals Open ocean dead zones in the tropical North Atlantic Ocean

2015 ◽  
Vol 12 (8) ◽  
pp. 2597-2605 ◽  
Author(s):  
J. Karstensen ◽  
B. Fiedler ◽  
F. Schütte ◽  
P. Brandt ◽  
A. Körtzinger ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Atlantic Ocean ◽  
Dead Zone ◽  
Marine Ecosystem ◽  
High Surface ◽  
Open Ocean ◽  
Depth Range ◽  
Low Oxygen ◽  
Dead Zones ◽  
Tropical North Atlantic

Abstract. Here we present first observations, from instrumentation installed on moorings and a float, of unexpectedly low (<2 μmol kg−1) oxygen environments in the open waters of the tropical North Atlantic, a region where oxygen concentration does normally not fall much below 40 μmol kg−1. The low-oxygen zones are created at shallow depth, just below the mixed layer, in the euphotic zone of cyclonic eddies and anticyclonic-modewater eddies. Both types of eddies are prone to high surface productivity. Net respiration rates for the eddies are found to be 3 to 5 times higher when compared with surrounding waters. Oxygen is lowest in the centre of the eddies, in a depth range where the swirl velocity, defining the transition between eddy and surroundings, has its maximum. It is assumed that the strong velocity at the outer rim of the eddies hampers the transport of properties across the eddies boundary and as such isolates their cores. This is supported by a remarkably stable hydrographic structure of the eddies core over periods of several months. The eddies propagate westward, at about 4 to 5 km day−1, from their generation region off the West African coast into the open ocean. High productivity and accompanying respiration, paired with sluggish exchange across the eddy boundary, create the "dead zone" inside the eddies, so far only reported for coastal areas or lakes. We observe a direct impact of the open ocean dead zones on the marine ecosystem as such that the diurnal vertical migration of zooplankton is suppressed inside the eddies.

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