scholarly journals Thermocline state change in the Eastern Equatorial Pacific during the late Pliocene/early Pleistocene intensification of Northern Hemisphere Glaciation

2017 ◽  
Author(s):  
Kim A. Jakob ◽  
Jörg Pross ◽  
Christian Scholz ◽  
Jens Fiebig ◽  
Oliver Friedrich
Keyword(s):  
Northern Hemisphere ◽  
Equatorial Pacific ◽  
Early Pleistocene ◽  
Trade Wind ◽  
Thermocline Depth ◽  
State Change ◽  
Final Phase ◽  
Late Pliocene ◽  
Eastern Equatorial Pacific ◽  
Earth’S Climate

Abstract. The late Pliocene/early Pleistocene intensification of Northern Hemisphere Glaciation (iNHG) ~ 2.5 million years ago (Marine Isotope Stages [MIS] 100–96) stands out as the most recent major tipping point in Earth's climate history. It strongly influenced oceanographic and climatic patterns including trade-wind and upwelling strength in the Eastern Equatorial Pacific (EEP). The thermocline depth in the EEP, in turn, plays a pivotal role in the evolution of short-term climate phenomena such the El Niño-Southern Oscillation, and thus bears important consequences for the Earth's climate system. However, thermocline dynamics in the EEP during to the iNHG have yet remained unclear. While numerous studies have suggested a link between a thermocline shoaling in the EEP and Northern Hemisphere ice growth, other studies have indicated a stable thermocline depth during iNHG, thereby excluding a causal relationship between thermocline dynamics and ice-sheet growth. In light of these contradictory views, we have generated geochemical (planktic foraminiferal δ18O, δ13C and Mg/Ca), sedimentological (sand-accumulation rates) and faunal (abundance data of thermocline-dwelling foraminifera) records for Ocean Drilling Program Site 849 located in the central part of the EEP. Our records span the interval from ~ 2.75 to 2.4 Ma (MIS G7–95), which is critical for understanding thermocline dynamics during the final phase of the iNHG. They document a thermocline shoaling from ~ 2.64 to 2.55 Ma (MIS G2–101) and a relatively shallow thermocline from ~ 2.55 Ma onwards (MIS 101–95). This indicates a state change in EEP thermocline depth shortly before the final phase of iNHG. Ultimately, our data support the hypothesis that (sub-)tropical thermocline shoaling may have contributed to the development of large Northern Hemisphere ice sheets.

scholarly journals Thermocline state change in the eastern equatorial Pacific during the late Pliocene/early Pleistocene intensification of Northern Hemisphere glaciation

2018 ◽  
Vol 14 (7) ◽  
pp. 1079-1095
Author(s):  
Kim Alix Jakob ◽  
Jörg Pross ◽  
Christian Scholz ◽  
Jens Fiebig ◽  
Oliver Friedrich
Keyword(s):  
Northern Hemisphere ◽  
Equatorial Pacific ◽  
Early Pleistocene ◽  
Trade Wind ◽  
Thermocline Depth ◽  
State Change ◽  
Final Phase ◽  
Late Pliocene ◽  
Eastern Equatorial Pacific ◽  
Earth’S Climate

Abstract. The late Pliocene/early Pleistocene intensification of Northern Hemisphere glaciation (iNHG) ∼2.5 million years ago (marine isotope stages, MIS, 100–96) stands out as an important tipping point in Earth's climate history, which strongly influenced oceanographic and climatic patterns including trade wind and upwelling strength in the eastern equatorial Pacific (EEP). The thermocline depth in the EEP, in turn, plays a pivotal role in the Earth's climate system: small changes in its depth associated with short-term climate phenomena such as the El Niño–Southern Oscillation can affect surface-water properties and the ocean–atmosphere exchange. However, thermocline dynamics in the EEP during the iNHG still remain unclear. While numerous studies have suggested a link between a thermocline shoaling in the EEP and Northern Hemisphere ice growth, other studies have indicated a stable thermocline depth during the iNHG; consequently, a causal relationship between thermocline dynamics and ice-sheet growth has been excluded. In light of these contradictory views, we have generated geochemical (planktic foraminiferal δ18O, δ13C and Mg ∕ Ca), sedimentological (sand accumulation rates) and faunal (abundance data of thermocline-dwelling foraminifera) records for Ocean Drilling Program Site 849 located in the central region of the EEP. Our records span the interval from ∼2.75 to 2.4 Ma (MIS G7–95), which is critical for understanding thermocline dynamics during the final phase of the iNHG. Our new records document a thermocline shoaling from ∼2.64 to 2.55 Ma (MIS G2–101) and a relatively shallow thermocline from ∼2.55 Ma onwards (MIS 101–95). This indicates a state change in thermocline depth at Site 849 shortly before the final phase of the iNHG. Ultimately, our data support the hypothesis that (sub-)tropical thermocline shoaling may have contributed to the development of large Northern Hemisphere ice sheets.

Ocean Response to Wind Variations, Warm Water Volume, and Simple Models of ENSO in the Low-Frequency Approximation

2010 ◽  
Vol 23 (14) ◽  
pp. 3855-3873 ◽  
Author(s):  
Alexey V. Fedorov
Keyword(s):  
Low Frequency ◽  
Equatorial Pacific ◽  
Warm Water ◽  
Water Volume ◽  
Thermocline Depth ◽  
Phase Lag ◽  
Eastern Equatorial Pacific ◽  
The Pacific ◽  
Warm Water Volume ◽  
Frequency Approximation

Abstract Physical processes that control ENSO are relatively fast. For instance, it takes only several months for a Kelvin wave to cross the Pacific basin (Tk ≈ 2 months), while Rossby waves travel the same distance in about half a year. Compared to such short time scales, the typical periodicity of El Niño is much longer (T ≈ 2–7 yr). Thus, ENSO is fundamentally a low-frequency phenomenon in the context of these faster processes. Here, the author takes advantage of this fact and uses the smallness of the ratio ɛk = Tk/T to expand solutions of the ocean shallow-water equations into power series (the actual parameter of expansion also includes the oceanic damping rate). Using such an expansion, referred to here as the low-frequency approximation, the author relates thermocline depth anomalies to temperature variations in the eastern equatorial Pacific via an explicit integral operator. This allows a simplified formulation of ENSO dynamics based on an integro-differential equation. Within this formulation, the author shows how the interplay between wind stress curl and oceanic damping rates affects 1) the amplitude and periodicity of El Niño and 2) the phase lag between variations in the equatorial warm water volume and SST in the eastern Pacific. A simple analytical expression is derived for the phase lag. Further, applying the low-frequency approximation to the observed variations in SST, the author computes thermocline depth anomalies in the western and eastern equatorial Pacific to show a good agreement with the observed variations in warm water volume. Ultimately, this approach provides a rigorous framework for deriving other simple models of ENSO (the delayed and recharge oscillators), highlights the limitations of such models, and can be easily used for decadal climate variability in the Pacific.

scholarly journals Equatorial Pacific peak in biological production regulated by nutrient and upwelling during the late Pliocene/early Pleistocene cooling

2013 ◽  
Vol 10 (3) ◽  
pp. 5535-5554
Author(s):  
J. Etourneau ◽  
R. S. Robinson ◽  
P. Martinez ◽  
R. Schneider
Keyword(s):  
Nutrient Supply ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Early Pleistocene ◽  
High Latitudes ◽  
Export Production ◽  
Eastern Equatorial Pacific ◽  
Nutrient Consumption ◽  
High Nutrient ◽  
High Nutrient Supply

Abstract. The largest increase in export production in the eastern Pacific of the last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of major climatic and oceanographic reorganization in the region. Here, we investigate the causes of this event using reconstructions of export production, nutrient supply and oceanic conditions across the Pliocene-Pleistocene in the eastern equatorial Pacific (EEP) for the last 3.2 Myr. Our results indicate that the export production peak corresponds to a cold interval marked by high nutrient supply relative to consumption, as revealed by the low bulk sedimentary 15N/14N (δ15N) and alkenone-derived sea surface temperature (SST) values. This ~ 0.6 million years long episode of enhanced delivery of nutrients to the surface of the EEP was predominantly initiated through the upwelling of nutrient-enriched water sourced in high latitudes. In addition, this phenomenon was likely promoted by the regional intensification of upwelling in response to the development of intense Walker and Hadley atmospheric circulations. Increased nutrient consumption in the polar oceans and enhanced denitrification in the equatorial regions restrained nutrient supply and availability and terminated the high export production event.

Reconstruction of environmental and climatic change during the late Pliocene and early Pleistocene in northwestern North America based on a new drill core from paleo-Lake Idaho

2020 ◽  
Author(s):  
Frederik Allstädt ◽  
Andreas Koutsodendris ◽  
Erwin Appel ◽  
Wolfgang Rösler ◽  
Alexander Prokopenko ◽  
...  
Keyword(s):  
North America ◽  
Northern Hemisphere ◽  
Moisture Transport ◽  
Snake River Plain ◽  
Early Pleistocene ◽  
Snake River ◽  
Depth Interval ◽  
Late Pliocene ◽  
River Plain ◽  
Northwestern North America

<p>The Pliocene to early Pleistocene yields a close analogy to near-future climate, with atmospheric <em>p</em>CO<sub>2</sub> between pre-industrial and anthropogenically perturbed levels as they may be reached in few decades. A sedimentary archive that is well suited to study Plio-Pleistocene climate dynamics in the terrestrial realm has recently become available through the ICDP-sponsored HOTSPOT project on the evolution of the Snake River Plain (Idaho, USA). At the Mountain Home site, HOTSPOT drilling has yielded the MHAFB11 core that comprises 635 m of fine-grained lacustrine sediments (Shervais et al. 2013). Based on the yet available paleomagnetic age control, these sediments span from the late Pliocene to the early Pleistocene, which makes them the first archive in continental North America that covers this time interval at one site. Based on their geographic position, the sediments from paleo-Lake Idaho can contribute to a better understanding of climate variability across the Plio-Pleistocene transition in western North America, notably with respect to the hypothesis that enhanced moisture transport into the higher latitudes of North America from ~2.7 Ma onwards allowed the initiation of Northern Hemisphere glaciation (Haug et al., 2005).</p><p>To gain insight into the paleoclimatic evolution of northwestern North America during the late Pliocene to early Pleistocene, we have palynologically analyzed 131 samples from the 732–439 m depth interval (corresponding to an age of ~2.8 to ~2 Ma) of the MHAFB11 core. The obtained palynological dataset, which has a mean temporal resolution of ~7 ka, documents that a <em>Pinus</em>-dominated coniferous forest biome prevailed in the catchment area of paleo-Lake Idaho throughout the study interval. However, percentages of pollen from conifer taxa decrease in the latest Pliocene before reaching consistently lower values in the early Pleistocene at ~2.4 Ma. In contrast, pollen taxa representing an open vegetation (e.g., <em>Artemisia</em>, Asteraceae) and deciduous trees (e.g., <em>Quercus</em>, <em>Betula</em> and <em>Alnus</em>) become increasingly abundant in the early Pleistocene (at ~2.4 Ma). We interpret this vegetation shift to an open mixed conifer/deciduous forest to be caused by wetter climate conditions. This interpretation is supported by quantitative climate estimates, which show a gradual increase in mean annual precipitation in the early Pleistocene. This trend towards wetter conditions supports the notion that enhanced moisture transport to northern North America from the subarctic Pacific Ocean contributed to the onset of Northern Hemisphere glaciation at ~2.7 Ma (Haug et al., 2005).</p><p> </p><p>References:</p><p>Haug, G.H., Ganopolski, A., Sigman, D.M., Rosell-Mele, A., Swann, G.E., Tiedemann, R., Jaccard, S.L., Bollmann, J., Maslin, M.A., Leng, M.J. and Eglinton, G., 2005. North Pacific seasonality and the glaciation of North America 2.7 million years ago. <em>Nature</em>, 433, 821-825.</p><p>Shervais, J.W., Schmitt, D.R., Nielson, D., Evans, J.P., Christiansen, E.H., Morgan, L.A., Shanks, P. W.C., Prokopenko, A.A., Lachmar, T., Liberty, L.M., Blackwell, D.D., Glen, J.M., Champion, D., Potter, K.E., Kessler, J., 2013. First Results from HOTSPOT: The Snake River Plain Scientific Drilling Project, Idaho, U.S.A. <em>Scientific</em> <em>Drilling,</em> 3, 36-45.</p><p> </p>

ENSO Dynamics in the E3SM-1-0, CESM2, and GFDL-CM4 Climate Models

2021 ◽  
pp. 1-59
Author(s):  
Han-Ching Chen ◽  
Fei-Fei Jin ◽  
Sen Zhao ◽  
Andrew T. Wittenberg ◽  
Shaocheng Xie
Keyword(s):  
Stress Responses ◽  
Climate Models ◽  
Phase Locking ◽  
Coupled Model ◽  
Convective Cloud ◽  
Equatorial Pacific ◽  
Thermocline Depth ◽  
Eastern Equatorial Pacific ◽  
Substantial Progress ◽  
Sea Surface Temperature Anomalies

AbstractThis study examines historical simulations of ENSO in the E3SM-1-0, CESM2, and GFDL-CM4 climate models, provided by three leading U.S. modeling centers as part of the Coupled Model Intercomparison Project phase 6 (CMIP6). These new models have made substantial progress in simulating ENSO’s key features, including: amplitude; timescale; spatial patterns; phase-locking; spring persistence barrier; and recharge oscillator dynamics. However, some important features of ENSO are still a challenge to simulate. In the central and eastern equatorial Pacific, the models’ weaker-than-observed subsurface zonal current anomalies and zonal temperature gradient anomalies serve to weaken the nonlinear zonal advection of subsurface temperatures, leading to insufficient warm/cold asymmetry of ENSO’s sea surface temperature anomalies (SSTA). In the western equatorial Pacific, the models’ excessive simulated zonal SST gradients amplify their zonal temperature advection, causing their SSTA to extend farther west than observed. The models underestimate both ENSO’s positive dynamic feedbacks (due to insufficient zonal wind stress responses to SSTA) and its thermodynamic damping (due to insufficient convective cloud shading of eastern Pacific SSTA during warm events); compensation between these biases leads to realistic linear growth rates for ENSO, but for somewhat unrealistic reasons. The models also exhibit stronger-than-observed feedbacks onto eastern equatorial Pacific SSTAs from thermocline depth anomalies, which accelerates the transitions between events and shortens the simulated ENSO period relative to observations. Implications for diagnosing and simulating ENSO in climate models are discussed.

scholarly journals Equatorial Pacific peak in biological production regulated by nutrient and upwelling during the late Pliocene/early Pleistocene cooling

2013 ◽  
Vol 10 (8) ◽  
pp. 5663-5670 ◽  
Author(s):  
J. Etourneau ◽  
R. S. Robinson ◽  
P. Martinez ◽  
R. Schneider
Keyword(s):  
Nutrient Supply ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Early Pleistocene ◽  
High Latitudes ◽  
Export Production ◽  
Eastern Equatorial Pacific ◽  
Nutrient Consumption ◽  
High Nutrient ◽  
High Nutrient Supply

Abstract. The largest increase in export production in the eastern Pacific of the last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of major climatic and oceanographic reorganization in the region. Here, we investigate the causes of this event using reconstructions of export production, nutrient supply and oceanic conditions across the Pliocene–Pleistocene in the eastern equatorial Pacific (EEP) for the last 3.2 Myr. Our results indicate that the export production peak corresponds to a cold interval marked by high nutrient supply relative to consumption, as revealed by the low bulk sedimentary 15N/14N (δ15N) and alkenone-derived sea surface temperature (SST) values. This ∼0.6 million year long episode of enhanced delivery of nutrients to the surface of the EEP was predominantly initiated through the upwelling of nutrient-enriched water sourced in high latitudes. In addition, this phenomenon was likely promoted by the regional intensification of upwelling in response to the development of intense Walker and Hadley atmospheric circulations. Increased nutrient consumption in the polar oceans and enhanced denitrification in the equatorial regions restrained nutrient supply and availability and terminated the high export production event.

Long Plio-Pleistocene Terrestrial Record of Climate Change and Mammal Turnover in Southern Spain

2001 ◽  
Vol 56 (3) ◽  
pp. 411-418 ◽  
Author(s):  
Jordi Agustı́ ◽  
Oriol Oms ◽  
Eduard Remacha
Keyword(s):  
Climate Change ◽  
Northern Hemisphere ◽  
Western Europe ◽  
Southern Spain ◽  
Early Pleistocene ◽  
Dry Period ◽  
Late Pliocene ◽  
Southeastern Spain ◽  
The Mediterranean

AbstractCyclostratigraphic analysis of the Pliocene Zújar section (Guadix-Baza Basin, southeastern Spain) has enabled the recognition of a number of climatically forced cycles reflecting alternating dry and wet periods. Peaks of aridity are recorded at ca. 3.95, 3.55, 3.2, 2.8, and 1.8 myr B.P. The first dry period at about 4.0 myr B.P. corresponds to the early Ruscinian Mammal age, while the second arid interval at about 3.6 myr B.P. corresponds to the establishment of the Mediterranean double seasonality. The significant mammal turnover between the late Ruscinian and early Villanyian stages is placed between chron 2An.2n and the very base of chron 2An.1n, coincident with the dry phase recognized at about 3.2 myr B.P. The fourth aridity maximum at 2.8 myr B.P. roughly coincides with the Equus event in western Europe and is probably related to the beginning of the glacial–interglacial dynamics in the Northern Hemisphere. Finally, the last dry peak at about 1.8 myr B.P. is probably related to the set of mammalian events characterizing the transition from the late Pliocene faunas to those of the early Pleistocene.

An Analysis of ENSO Prediction Skill in the CFS Retrospective Forecasts

2009 ◽  
Vol 22 (7) ◽  
pp. 1801-1818 ◽  
Author(s):  
Renguang Wu ◽  
Ben P. Kirtman ◽  
Huug van den Dool
Keyword(s):  
Wind Stress ◽  
Zonal Wind ◽  
Equatorial Pacific ◽  
Prediction Skill ◽  
Thermocline Depth ◽  
Zonal Wind Stress ◽  
Boreal Spring ◽  
Eastern Equatorial Pacific ◽  
Western Equatorial Pacific ◽  
Sst Anomalies

Abstract The present study documents the so-called spring prediction and persistence barriers in association with El Niño–Southern Oscillation (ENSO) in the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS) retrospective forecasts. It is found that the spring prediction and persistence barriers in the eastern equatorial Pacific sea surface temperature (SST) are preceded by a boreal winter barrier in the western equatorial Pacific zonal wind stress. The time of the persistence barrier is closely related to the time of the ENSO phase transition, but may differ from the time of the lowest variance. The seasonal change of the signal-to-noise ratio cannot explain the persistence barrier. While the noise may lead to a drop of skill around boreal spring in the western equatorial Pacific zonal wind stress, its impacts on the skill of eastern equatorial Pacific SST is small. The equatorial Pacific zonal winds display an excessive response to ENSO-related SST anomalies, which leads to a longer persistence in the equatorial Pacific thermocline depth anomalies and a delayed transition of the eastern equatorial Pacific SST anomalies. This provides an interpretation for the prediction skill drop in boreal spring in the eastern equatorial Pacific SST. The results suggest that improving the atmospheric model wind response to SST anomalies may reduce the spring prediction barrier.

scholarly journals Experimental Implementation of an Ensemble Adjustment Filter for an Intermediate ENSO Model

2007 ◽  
Vol 20 (18) ◽  
pp. 4638-4658 ◽  
Author(s):  
Alicia R. Karspeck ◽  
Jeffrey L. Anderson
Keyword(s):  
Interannual Variability ◽  
Wind Stress ◽  
Coupled Model ◽  
Equatorial Pacific ◽  
Thermocline Depth ◽  
Ensemble Size ◽  
Incomplete Observations ◽  
Eastern Equatorial Pacific ◽  
Experimental Implementation ◽  
Independent Observations

Abstract The assimilation of sea surface temperature (SST) anomalies into a coupled ocean–atmosphere model of the tropical Pacific is investigated using an ensemble adjustment Kalman filter (EAKF). The intermediate coupled model used here is the operational version of the Zebiak–Cane model, called LDEO5. The assimilation is applied as a means of estimating the true state of the system in the presence of incomplete observations of the state. In the first part of this study assimilation is performed under the “perfect model” assumption, where SST observations are synthetically derived from a trajectory of the model. The focus is on how and why changes in the filter parameters (ensemble size, covariance localization, and covariance inflation) affect the quality of the analysis. It is shown that isotropic covariance localization does not benefit the analysis even when a small number of ensemble members are used. These results suggest that destruction of the “balance” between variables caused by localization is more detrimental than spurious correlation due to small ensemble size. In the second part of this study the EAKF is used to assimilate an independent dataset of SST observations. The EAKF/Zebiak–Cane assimilation system is able to correctly estimate the phase and intensity of ENSO, as measured by the average SST anomaly in the eastern equatorial Pacific. A comparison of the analysis herein to independent wind stress and thermocline depth datasets suggests that even with the assimilation of only SST observations it is possible to reproduce over 70% of the interannual variability of thermocline depth in the eastern equatorial Pacific and off the coast of the Philippine Islands. The interannual variability of zonal wind stress in the central and western equatorial Pacific is also well correlated with independent observations (R > 0.75).

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