Late cretaceous ocean circulation in the south Atlantic and Pacific oceans

2019 ◽  
Author(s):  
◽  
Shannon Haynes
Keyword(s):  
Indian Ocean ◽  
Ocean Circulation ◽  
Late Cretaceous ◽  
North Atlantic ◽  
High Latitude ◽  
Climate Model ◽  
South Atlantic ◽  
Regional Studies ◽  
Circulation Patterns ◽  
Insight Into

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Cooling during the last 15 million years of the Cretaceous is widely believed to have resulted in a reorganization of ocean circulation, with cooler periods being associated with deep ocean convection in high latitude regions (e.g., Robinson et al., 2010; MacLeod et al., 2011; Robinson and Vance, 2012; Jung et al., 2013). Understanding the relationship between climate change and sub-surface ocean circulation patterns, and gaining further insight into how circulation dynamics were influenced by the unique Cretaceous paleobathymetry is crucial to furthering our understanding of global climate dynamics during the Late Cretaceous. To provide further insight into Late Cretaceous ocean circulation we used neodymium isotopes as a tool to infer past ocean circulation patterns. Neodymium was extracted from fossilized fish teeth and bone fragments from bulk rock samples at 26 different sites (4 Pacific, 12 South Atlantic, 3 North Atlantic, 3 proto-Indian Ocean). We present two regional studies that focus on Campanian (84-72 Ma) and Maastrichtian (72-66 Ma) circulation patterns in the Pacific (Chapter 2) and South Atlantic (Chapter 3) Oceans. These chapters argue that, by the end of the Cretaceous, climate had cooled enough to support high latitude convection but also that circulation patterns were tightly controlled by bathymetry. To investigate the global implications of these two regional studies we also present preliminary neodymium isotopic data from several sites in the North Atlantic and proto-Indian Ocean (Chapter 4). Further, neodymium isotopic trends were compared to climate model simulations as well as to previously published neodymium, carbon, and oxygen isotopic records.

scholarly journals South Atlantic island record reveals a South Atlantic response to the 8.2 kyr event

2007 ◽  
Vol 3 (3) ◽  
pp. 729-753 ◽  
Author(s):  
K. Ljung ◽  
S. Björck ◽  
H. Renssen ◽  
D. Hammarlund
Keyword(s):  
North Atlantic ◽  
Energy Transport ◽  
Climate Model ◽  
South Atlantic ◽  
Laurentide Ice Sheet ◽  
Climate Fluctuations ◽  
The North ◽  
Central South ◽  
Atlantic Island ◽  
8.2 Kyr Event

Abstract. One of the most distinct climate fluctuations during the Holocene is the short and rapid event centred around 8200 years ago, the 8.2 kyr event, which was most likely triggered by glacial melt-water forcing from the receding Laurentide ice-sheet. Evidence for this cooling has primarily been reported from sites around the North Atlantic, but an increasing number of observations imply a more wide-spread occurrence. Palaeoclimate archives from the Southern Hemisphere have hitherto failed to uncover a distinct climatic anomaly associated with the 8.2 kyr event. Here we present a lake sediment record from Nightingale Island in the central South Atlantic showing enhanced precipitation between 8275 and 8025 cal. yrs BP, most likely as a consequence of increased sea surface temperature (SST). We show that this is consistent with climate model projections of a warming of the South Atlantic in response to reduced north-ward energy transport during the 8.2 kyr event.

scholarly journals Fingerprints of changes in the terrestrial carbon cycle in response to large reorganizations in ocean circulation

2010 ◽  
Vol 6 (5) ◽  
pp. 1811-1852 ◽  
Author(s):  
A. Bozbiyik ◽  
M. Steinacher ◽  
F. Joos ◽  
T. F. Stocker
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Climate Model ◽  
Carbon Stocks ◽  
Meridional Overturning Circulation ◽  
Climate Conditions ◽  
Tropical Regions ◽  
The North ◽  
Northern Latitudes

Abstract. CO2 and carbon cycle changes in the land, ocean and atmosphere are investigated using the comprehensive carbon cycle-climate model NCAR CSM1.4-carbon. Ensemble simulations are forced with freshwater perturbations applied at the North Atlantic and Southern Ocean deep water formation sites under pre-industrial climate conditions. As a result, the Atlantic Meridional Overturning Circulation reduces in each experiment to varying degrees. The physical climate fields show changes that are well documented in the literature but there is a clear distinction between northern and southern perturbations. Changes in the physical variables affect, in return, the land and ocean biogeochemical cycles and cause a reduction, or an increase, in the atmospheric CO2 by up to 20 ppmv, depending on the location of the perturbation. In the case of a North Atlantic perturbation, the land biosphere reacts with a strong reduction in carbon stocks in some tropical locations and in high northern latitudes. In contrast, land carbon stocks tend to increase in response to a southern perturbation. The ocean is generally a sink of carbon although large re-organizations occur throughout various basins. The response of the land biosphere is strongest in the tropical regions due to a shift of the Intertropical Convergence Zone. The carbon fingerprints of this shift, either to the south or to the north depending on where the freshwater is applied, can be found most clearly in South America. For this reason, a compilation of various paleoclimate proxy records of Younger Dryas precipitation changes are compared with our model results.

Co-variability of salinity and temperature changes in the North Atlantic

2021 ◽  
Author(s):  
Levke Caesar ◽  
Gerard McCarthy
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Climate Model ◽  
Surface Fluxes ◽  
Meridional Overturning Circulation ◽  
Geophysical Research ◽  
Overturning Circulation ◽  
The North ◽  
Cold Anomaly ◽  
The North Atlantic

<p>While there is increasing paleoclimatic evidence that the Atlantic Meridional Overturning Circulation (AMOC) has weakened over the last one to two hundred years (Caesar et al., 2018; Thornalley et al., 2018), this is not confirmed by climate model simulations. Instead, the new simulations from the 6th Coupled Model Intercomparison Project (CMIP6) show a slight strengthening of the multimodel mean AMOC from 1850 until about 1985 (Menary et al., 2020), attributed to anthropogenic aerosol forcing. Arguing for a recent weakening of the AMOC, some studies attribute the emergence of the North Atlantic warming hole as a sign of the reduced meridional heat transport associated with a weaker AMOC (e.g. Caesar et al., 2018), yet this cold anomaly has also been interpreted as being aerosol-forced (Booth et al., 2012) and therefore not necessarily a sign of a weakening AMOC but rather a possible driver of a strengthening of the AMOC.</p><p>Looking beyond temperature, a fresh anomaly has recently emerged in the subpolar North Atlantic (Holliday et al., 2020). While a strengthening AMOC has been linked with an increase in salinity in the subpolar gyre region (Menary et al., 2013), an AMOC weakening would, due to the salt-advection feedback, likely lead to a reduction in salinity in the North Atlantic region. To shed some light on the question of whether the cold anomaly is internally (AMOC) or externally (aerosol-forced) driven we consider the co-variability of salinity and temperature in the North Atlantic in respect of changes in surface fluxes or alternate drivers.</p><p> </p><p>References</p><p>Booth, B.B.B., Dunstone, N.J., Halloran, P.R., Andrews, T. and Bellouin, N., 2012. Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability. Nature, 484(7393): 228–232.</p><p>Caesar, L., Rahmstorf, S., Robinson, A., Feulner, G. and Saba, V., 2018. Observed fingerprint of a weakening Atlantic Ocean overturning circulation. Nature, 556(7700): 191-196.</p><p>Holliday, N.P., Bersch, M., Berx, B., Chafik, L., Cunningham, S., Florindo-López, C., Hátún, H., Johns, W., Josey, S.A., Larsen, K.M.H., Mulet, S., Oltmanns, M., Reverdin, G., Rossby, T., Thierry, V., Valdimarsson, H. and Yashayaev, I., 2020. Ocean circulation causes the largest freshening event for 120 years in eastern subpolar North Atlantic. Nature Communications, 11(1): 585.</p><p>Menary, M.B., Roberts, C.D., Palmer, M.D., Halloran, P.R., Jackson, L., Wood, R.A., Müller, W.A., Matei, D. and Lee, S.-K., 2013. Mechanisms of aerosol-forced AMOC variability in a state of the art climate model. Journal of Geophysical Research: Oceans, 118(4): 2087-2096.</p><p>Menary, M.B., Robson, J., Allan, R.P., Booth, B.B.B., Cassou, C., Gastineau, G., Gregory, J., Hodson, D., Jones, C., Mignot, J., Ringer, M., Sutton, R., Wilcox, L. and Zhang, R., 2020. Aerosol-Forced AMOC Changes in CMIP6 Historical Simulations. Geophysical Research Letters, 47(14): e2020GL088166.</p><p>Thornalley, D.J.R., Oppo, D.W., Ortega, P., Robson, J.I., Brierley, C.M., Davis, R., Hall, I.R., Moffa-Sanchez, P., Rose, N.L., Spooner, P.T., Yashayaev, I. and Keigwin, L.D., 2018. Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years. Nature, 556(7700): 227-230.</p>

scholarly journals Fingerprints of changes in the terrestrial carbon cycle in response to large reorganizations in ocean circulation

2011 ◽  
Vol 7 (1) ◽  
pp. 319-338 ◽  
Author(s):  
A. Bozbiyik ◽  
M. Steinacher ◽  
F. Joos ◽  
T. F. Stocker ◽  
L. Menviel
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Climate Model ◽  
Carbon Stocks ◽  
Meridional Overturning Circulation ◽  
Climate Conditions ◽  
Tropical Regions ◽  
Proxy Records ◽  
The North

Abstract. CO2 and carbon cycle changes in the land, ocean and atmosphere are investigated using the comprehensive carbon cycle-climate model NCAR CSM1.4-carbon. Ensemble simulations are forced with freshwater perturbations applied at the North Atlantic and Southern Ocean deep water formation sites under pre-industrial climate conditions. As a result, the Atlantic Meridional Overturning Circulation reduces in each experiment to varying degrees. The physical climate fields show changes qualitatively in agreement with results documented in the literature, but there is a clear distinction between northern and southern perturbations. Changes in the physical variables, in turn, affect the land and ocean biogeochemical cycles and cause a reduction, or an increase, in the atmospheric CO2 concentration by up to 20 ppmv, depending on the location of the perturbation. In the case of a North Atlantic perturbation, the land biosphere reacts with a strong reduction in carbon stocks in some tropical locations and in high northern latitudes. In contrast, land carbon stocks tend to increase in response to a southern perturbation. The ocean is generally a sink of carbon although large reorganizations occur throughout various basins. The response of the land biosphere is strongest in the tropical regions due to a shift of the Intertropical Convergence Zone. The carbon fingerprints of this shift, either to the south or to the north depending on where the freshwater is applied, can be found most clearly in South America. For this reason, a compilation of various paleoclimate proxy records of Younger Dryas precipitation changes are compared with our model results. The proxy records, in general, show good agreement with the model's response to a North Atlantic freshwater perturbation.

scholarly journals An Intrinsic Mode of Interannual Variability in the Indian Ocean

2017 ◽  
Vol 47 (3) ◽  
pp. 701-719 ◽  
Author(s):  
Christopher L. Wolfe ◽  
Paola Cessi ◽  
Bruce D. Cornuelle
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Ocean Circulation ◽  
Baroclinic Instability ◽  
Ocean Model ◽  
South Atlantic ◽  
Global Ocean ◽  
Leeuwin Current ◽  
The Indian Ocean ◽  
Atmospheric State

AbstractAn intrinsic mode of self-sustained, interannual variability is identified in a coarse-resolution ocean model forced by an annually repeating atmospheric state. The variability has maximum loading in the Indian Ocean, with a significant projection into the South Atlantic Ocean. It is argued that this intrinsic mode is caused by baroclinic instability of the model’s Leeuwin Current, which radiates out to the tropical Indian and South Atlantic Oceans as long Rossby waves at a period of 4 yr. This previously undescribed mode has a remarkably narrowband time series. However, the variability is not synchronized with the annual cycle; the phase of the oscillation varies chaotically on decadal time scales. The presence of this internal mode reduces the predictability of the ocean circulation by obscuring the response to forcing or initial condition perturbations. The signature of this mode can be seen in higher-resolution global ocean models driven by high-frequency atmospheric forcing, but altimeter and assimilation analyses do not show obvious signatures of such a mode, perhaps because of insufficient duration.

scholarly journals Progress in understanding of Indian Ocean circulation, variability, air-sea exchange and impacts on biogeochemistry

2021 ◽  
Author(s):  
Helen E. Phillips ◽  
Amit Tandon ◽  
Ryo Furue ◽  
Raleigh Hood ◽  
Caroline Ummenhofer ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Climate Variability ◽  
Ocean Circulation ◽  
Large Scale ◽  
New Technologies ◽  
Heat Content ◽  
Deep Ocean ◽  
Small Scale ◽  
Circulation Patterns ◽  
The Indian Ocean

Abstract. Over the past decade, our understanding of the Indian Ocean has advanced through concerted efforts toward measuring the ocean circulation and its water properties, detecting changes in water masses, and linking physical processes to ecologically important variables. New circulation pathways and mechanisms have been discovered, which control atmospheric and oceanic mean state and variability. This review brings together new understanding of the ocean-atmosphere system in the Indian Ocean since the last comprehensive review, describing the Indian Ocean circulation patterns, air-sea interactions and climate variability. The second International Indian Ocean Expedition (IIOE-2) and related efforts have motivated the application of new technologies to deliver higher-resolution observations and models of Indian Ocean processes. As a result we are discovering the importance of small scale processes in setting the large-scale gradients and circulation, interactions between physical and biogeochemical processes, interactions between boundary currents and the interior, and between the surface and the deep ocean. In the last decade we have seen rapid warming of the Indian Ocean overlaid with extremes in the form of marine heatwaves. These events have motivated studies that have delivered new insight into the variability in ocean heat content and exchanges in the Indian Ocean, and climate variability on interannual to decadal timescales.This synthesis paper reviews the advances in these areas in the last decade.

Characteristics and variability of ocean ventilation in the high-latitude North Atlantic in an eddy-permitting ocean model

2021 ◽  
Author(s):  
Helen L. Johnson ◽  
Graeme MacGilchrist ◽  
David P. Marshall ◽  
Camille Lique ◽  
Matthew Thomas ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Mixed Layer ◽  
North Atlantic ◽  
High Latitude ◽  
Circulation Model ◽  
Open Ocean ◽  
Labrador Sea ◽  
Surface Mixed Layer ◽  
Atmospheric Forcing ◽  
Boundary Current

<p>A substantial fraction of the deep ocean is ventilated in the high latitude North Atlantic. As a result, the region plays a crucial role in transient climate change through the uptake of carbon dioxide and heat. We investigate the nature of ventilation in the high latitude North Atlantic in an eddy-permitting numerical ocean circulation model using a set of comprehensive Lagrangian trajectory experiments. Backwards-in-time trajectories from a model-defined ‘North Atlantic Deep Water’ (NADW) reveal the times and locations of subduction from the surface mixed layer at high temporal and spatial resolution. The major fraction (∼60%) of NADW ventilation results from subduction directly into the Labrador Sea boundary current, with a smaller fraction (∼25%) arising from open ocean deep convection in the Labrador Sea. There is a notable absence of ventilation arising from subduction in the Greenland–Iceland–Norwegian Seas, due to the re-entrainment of those waters as they move southward. Temporal variability in ventilation arises both from changes in subduction — driven by large-scale atmospheric forcing — and from year-to-year changes in the subsurface retention of newly subducted water, the result of an inter-annual equivalent of Stommel’s mixed layer demon. This interannual demon operates most effectively in the open ocean where newly subducted water is slow to escape its region of subduction. Thus, while subduction in the boundary current dominates NADW ventilation, processes in the open ocean set the variability, mediating the translation of inter-annual variations in atmospheric forcing to the ocean interior.</p>

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