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Observations of anthropogenic global warming

Papers on late Pliocene cooling event (3Ma)

Posted by Ari Jokimäki on April 16, 2010

This is a list of papers on late Pliocene cooling event that happened about 3 million years ago and caused the glaciation of the northern hemisphere. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Mid-Pliocene Asian monsoon intensification and the onset of Northern Hemisphere glaciation – Zhang et al. (2009) “Here we present a key low-latitude climate record, the high-resolution Asian monsoon precipitation variability for the past five million years, reconstructed from South China Sea sediments. Our results, with supporting evidence from other records, indicate significant mid-Pliocene Asian monsoon intensification, preceding the initiation of NHG at ca. 2.7 Ma ago. This 1.4-million-year-long monsoon intensification probably enhanced monsoon-induced Asian continental erosion and chemical weathering and in the process left fingerprints in marine calcium isotopes. Furthermore, increased rock weathering and/or organic carbon burial probably lowered the contemporary atmospheric CO2 and may have triggered the NHG onset.”

Late Pliocene Greenland glaciation controlled by a decline in atmospheric CO2 levels – Lunt et al. (2008) “Several hypotheses have been proposed to explain this increase in Northern Hemisphere glaciation during the Late Pliocene. Here we use a fully coupled atmosphere–ocean general circulation model and an ice-sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the Greenland ice sheet in particular. We find that Greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the Late Pliocene. By contrast, our model results suggest that climatic shifts associated with the tectonically driven closure of the Panama seaway, with the termination of a permanent El Niño state or with tectonic uplift are not large enough to contribute significantly to the growth of the Greenland ice sheet; moreover, we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the Earth’s orbit.” [Full text]

Slow dynamics of the Northern Hemisphere glaciation – Mudelsee & Raymo (2005) “We use 45 δ18O records from benthic and planktonic foraminifera and globally distributed sites to reconstruct the dynamics of NHG initiation. We compare δ18O amplitudes with those of temperature proxy records and estimate a global ice volume–related increase of 0.4‰, equivalent to an overall sea level lowering of 43 m. We find the NHG started significantly earlier than previously assumed, as early as 3.6 Ma, and ended at 2.4 Ma. This long-term increase points to slow, tectonic forcing such as closing of ocean gateways or mountain building as the root cause of the NHG.” [Full text]

Final closure of Panama and the onset of northern hemisphere glaciation – Bartoli et al. (2005) “In contrast, our new submillennial-scale paleoceanographic records from the Pliocene North Atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation (NHG), since it was linked to a 2–3 °C surface water warming during warm stages from 2.95 to 2.82 Ma. These records support previous models [G.H. Haug, R. Tiedemann, Effect of the formation of the Isthmus of Panama on Atlantic Ocean thermohaline circulation, Nature 393 (1998) 673–676. [2]] claiming that the final closure of the Panama Isthmus (3.0– 2.5 Ma [J. Groeneveld S. Steph, R. Tiedemann, D. Nürnberg, D. Garbe-Schönberg, The final closure of the Central American Seaway, Geology, in prep. [3]]) induced an increased poleward salt and heat transport. Associated strengthening of North Atlantic Thermohaline Circulation and in turn, an intensified moisture supply to northern high latitudes resulted in the build-up of NHG, finally culminating in the great, irreversible “climate crash” at marine isotope stage G6 (2.74 Ma). In summary, there was a two-step threshold mechanism that marked the onset of NHG with glacial-to-interglacial cycles quasi-persistent until today.” [Full text]

Regional climate shifts caused by gradual global cooling in the Pliocene epoch – Ravelo et al. (2004) “Here we compare climate records from high latitudes, subtropical regions and the tropics, indicating that the onset of large glacial/interglacial cycles did not coincide with a specific climate reorganization event at lower latitudes. The regional differences in the timing of cooling imply that global cooling was a gradual process, rather than the response to a single threshold or episodic event as previously suggested. We also find that high-latitude climate sensitivity to variations in solar heating increased gradually, culminating after cool tropical and subtropical upwelling conditions were established two million years ago.” [Full text]

Role of tropics in changing the response to Milankovich forcing some three million years ago – Philander & Fedorov (2003) “Throughout the Cenozoic the Earth experienced global cooling that led to the appearance of continental glaciers in high northern latitudes around 3 Ma ago. At approximately the same time, cold surface waters first appeared in regions that today have intense oceanic upwelling: the eastern equatorial Pacific and the coastal zones of southwestern Africa and California. There was furthermore a significant change in the Earth’s response to Milankovich forcing: obliquity signals became large, but those associated with precession and eccentricity remained the same. The latter change in the Earth’s response can be explained by hypothesizing that the global cooling during the Cenozoic affected the thermal structure of the ocean; it caused a gradual shoaling of the thermocline. Around 3 Ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions. This brought into play feedbacks involving ocean-atmosphere interactions of the type associated with El Niño and also mechanisms by which high-latitude surface conditions can influence the depth of the tropical thermocline. Those feedbacks and mechanisms can account for the amplification of the Earth’s response to periodic variations in obliquity (at a period of 41K) without altering the response to Milankovich forcing at periods of 100,000 and 23,000 years. This hypothesis is testable. If correct, then in the tropics and subtropics the response to obliquity variations is in phase with, and corresponds to, El Niño conditions when tilt is large and La Niña conditions when tilt is small.” [Full text]

The contribution of orbital forcing to the progressive intensification of northern hemisphere glaciation – Maslin et al. (1998) “In this study, we reconstruct the timing of the onset of Northern Hemisphere glaciation. This began in the late Miocene with a significant build-up of ice on Southern Greenland. However, progressive intensification of glaciation did not begin until 3.5-3 Ma, when the Greenland ice sheet expanded to include Northern Greenland. Following this stage we suggest that the Eurasian Arctic and Northeast Asia were glaciated at approximately 2.74 Ma, 40 ka before the glaciation of Alaska (2.70 Ma) and about 200 ka before significant glaciation of the North East American continent (2.54 Ma). We also review the suggested causes of Northern Hemisphere glaciation. Tectonic changes, such as the uplift of the Himalayan and Tibetan Plateau, the deepening of the Bering Strait and the emergence of the Panama Isthmus, are too gradual to account entirely for the speed of Northern Hemisphere glaciation. We, therefore, postulate that tectonic changes may have brought global climate to a critical threshold, but the relatively rapid variations in the Earth’s orbital parameters and thus insolation, triggered the intensification of Northern Hemisphere glaciation. This theory is supported by computer simulations, which despite the relative simplicity of the model and the approximation of some factors (e.g. using a linear carbon dioxide scenario, neglecting the geographical difference between the Pliocene and the present) suggest that it is possible to build-up Northern Hemisphere ice sheets, between 2.75 and 2.55 Ma, by varying only the insolation controlled by the orbital parameters.” [Full text]

The progressive intensification of northern hemisphere glaciation as seen from the North Pacific – Maslin et al. (1996) “Ocean Drilling Project (ODP) site 882 (50°22′N, 167°36′E) provides the first high-resolution GRAPE density, magnetic susceptibility, carbonate, opal and foraminifera (planktonic and benthic) stable isotopes records between 3.2 and 2.4 Ma in the Northwest Pacific. We observed a dramatic increase in ice rafting debris at site 882 at 2.75 Ma, which is coeval with that found in the Norwegian Sea, suggesting that the Eurasian Arctic and Northeast Asia were significantly glaciated from 2.75 Ma onwards. Prior to 2.75 Ma planktonic foraminifera δ18O records indicate a warming or freshening trend of 4°C or 2‰ over 80 ka. If this is interpreted as a warm pre-glacial Pliocene North Pacific, it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet. The dramatic drop in sea surface temperatures (SST>7.5°C) at 2.75 Ma ended this suggested period of enhanced SST and thus the proposed moisture pump. Moreover, at 2.79 and 2.73 Ma opal mass accumulation rates (MAR) decrease in two steps by five fold and is accompanied by a more gradual long-term decrease in CaCO3 MARs. Evidence from the Southern Ocean (ODP site 704) indicates that just prior to 2.6 Ma there is a massive increase in opal MARs, the opposite to what is found in the North Pacific. This indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget, possibly caused by changes in deep ocean circulation. The initiation of northern hemisphere glaciation occurred in the late Miocene with a significant build up of ice on southern Greenland. However, the progressive intensification did not occur until 3.5–3 Ma when the Greenland ice sheet expanded to include northern Greenland. Following this stage we suggest that the Eurasian Arctic and Northeast Asia glaciated at 2.75 Ma, approximately 100 ka before the glaciation of Alaska (2.65 Ma) and 200 ka before the glaciation of the North East American continent (2.54 Ma).”

The Initiation of Northern Hemisphere Glaciation – Raymo (1994) A review article. “In this paper, the climate transition from the warm mid-Pliocene (around 3.2 Ma) to the onset of northern hemisphere ice ages around 2.4 Ma is examined. Evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe.” [Full text]

Tectonic forcing of late Cenozoic climate – Raymo & Ruddiman (1992) “Global cooling in the Cenozoic, which led to the growth of large continental ice sheets in both hemispheres, may have been caused by the uplift of the Tibetan plateau and the positive feedbacks initiated by this event. In particular, tectonically driven increases in chemical weathering may have resulted in a decrease of atmospheric C02 concentration over the past 40 Myr.” [Full text]

The cause of the Late Cenozoic Northern Hemisphere glaciations: a climate change enigma – Hay (1992) “The ultimate cause of the onset of glaciations remains elusive, but in the case of northem hemisphere glaciation it is probable that several factors acted in combination. General global cooling resulted from reduction of atmospheric C02 by weathering of silicate rocks exposed by erosion of late Cenozoic uplifts. Uplifts in south Asia, southwestern North America and Scandinavia occurred at distances appropriate for the generation of quasi-permanent Rossby waves in the atmosphere. The resulting winds, given suitable moisture sources, were favourable for causing large-scale precipitation at mid-latitudes on the northern continents. Moisture sources were provided by the closure of the Central American isthmus. Gulf Stream flow increased, carrying warm subtropical waters to high latitudes. The Denmark Strait deepened permitting greater outflow of deep water from the Norwegian-Greenland Sea. The relative importance of each of these factors should be investigated by additional atmospheric and ocean climate model sensitivity studies.”

Global Wind-Induced Change of Deep-Sea Sediment Budgets, New Ocean Production and CO2 Reservoirs ca. 3.3-2.35 Ma BP – Sarnthein & Fenner (1988) “The late Pliocene phase of large-scale climatic deterioration about 3.2-2.4 Ma BP is well documented in a number of (benthic) δ18O records. To test the global implications of this event, we have mapped the distribution patterns of various sediment variables in the Pacific and Atlantic Oceans during two time slices, 3.4-3.18 and 2.43-2.33 Ma BP. The changes of bulk sedimentation and bulk sediment accumulation rates are largely explained by the variations of CaCO3-accumulation rates (and the accumulation rates of the complementary siliciclastic sediment fraction near continents in higher latitudes). During the late Pliocene, the CaCO3-accumulation rate increased along the equatorial Pacific and Atlantic and in the northeastern Atlantic, but decreased elsewhere. The accumulation rate of organic carbon (Corg) and net palaeoproductivity also increased below the high-productivity belts along the equator and the eastern continental margins. From these patterns we may conclude that (trade-) wind-induced upwelling zones and upwelling productivity were much enhanced during that time. This change led to an increased transfer of CO2 from the surface ocean to the ocean deep water and to a reduction of evaporation, which resulted in an aridification of the Saharan desert belt as depicted in the dust sediments off northwest Africa.”

Oxygen isotope and palaeomagnetic evidence for early Northern Hemisphere glaciation – Shackleton & Opdyke (1977) “Oxygen isotope and palaeomagnetic analysis of the lower half of LDGO piston core V28−179 shows that glacial−interglacial fluctuations have characterised Earth’s climate for the past 3.2 Myr, before which there was a period of stable ‘interglacial’ or ‘preglacial’ climate. The scale of glaciations increased about 2.5 Myr ago.”


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