Orbital and suborbital‐scale variations of productivity and sea surface conditions in the Gulf of Alaska during the past 54,000 years: Impact of iron fertilization by icebergs and meltwater

In simulations of the climate during the Last Glacial Maximum (LGM), we employ two different isotope-enabled atmospheric general circulation models (NCAR iCAM3 and MPI ECHAM6-wiso) and use simulated (by coupled climate models) as well as reconstructed (from a new global climatology of the ocean surface duing the LGM, GLOMAP) surface conditions.The resulting atmospheric fields reflect the more pronounced structure and gradients in the reconstructions, for example, the precipitation is more depleted in oxygen-18 in the high latitudes and more enriched in low latitudes, especially in the tropical convective regions over the maritime continent in the equatorial Pacific and Indian Oceans and over the equatorial Atlantic Ocean. Furthermore, at the sites of ice cores and speleothems, the model-data fit improves in terms of the coefficients of determination and root-mean square errors.In additional sensitivity experiments, we also use the climatologies by Annan and Hargreaves (2013) and Tierney et al. (2020) and consider the impact of changes in reconstructed sea-ice extent and the global-mean sea-surface temperature.Our findings imply that the correct simulation or reconstruction of patterns and gradients in sea-surface conditions are crucial for a successful comparison to oxygen-isotope data from ice cores and speleothems.

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Palynological evidence of sea-surface conditions in the Barents Sea off northeast Svalbard during the postglacial period

Quaternary Research ◽

10.1017/qua.2020.2 ◽

2020 ◽

pp. 1-15

Author(s):

Camille Brice ◽

Anne de Vernal ◽

Elena Ivanova ◽

Simon van Bellen ◽

Nicolas Van Nieuwenhove

Keyword(s):

Sea Ice ◽

Surface Waters ◽

Barents Sea ◽

Ice Cover ◽

Atlantic Water ◽

Transitional Period ◽

Sea Surface ◽

Sea Surface Salinity ◽

Surface Conditions ◽

The Barents Sea

Abstract Postglacial changes in sea-surface conditions, including sea-ice cover, summer temperature, salinity, and productivity were reconstructed from the analyses of dinocyst assemblages in core S2528 collected in the northwestern Barents Sea. The results show glaciomarine-type conditions until about 11,300 ± 300 cal yr BP and limited influence of Atlantic water at the surface into the Barents Sea possibly due to the proximity of the Svalbard-Barents Sea ice sheet. This was followed by a transitional period generally characterized by cold conditions with dense sea-ice cover and low-salinity pulses likely related to episodic freshwater or meltwater discharge, which lasted until 8700 ± 700 cal yr BP. The onset of “interglacial” conditions in surface waters was marked by a major change in dinocyst assemblages, from dominant heterotrophic to dominant phototrophic taxa. Until 4100 ± 150 cal yr BP, however, sea-surface conditions remained cold, while sea-surface salinity and sea-ice cover recorded large amplitude variations. By ~4000 cal yr BP optimum sea-surface temperature of up to 4°C in summer and maximum salinity of ~34 psu suggest enhanced influence of Atlantic water, and productivity reached up to 150 gC/m2/yr. After 2200 ± 1300 cal yr BP, a distinct cooling trend accompanied by sea-ice spreading characterized surface waters. Hence, during the Holocene, with exception of an interval spanning about 4000 to 2000 cal yr BP, the northern Barents Sea experienced harsh environments, relatively low productivity, and unstable conditions probably unsuitable for human settlements.

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Atmospheric dynamics drive most interannual U.S. droughts over the last millennium

Science Advances ◽

10.1126/sciadv.aay7268 ◽

2020 ◽

Vol 6 (32) ◽

pp. eaay7268

Author(s):

M. P. Erb ◽

J. Emile-Geay ◽

G. J. Hakim ◽

N. Steiger ◽

E. J. Steig

Keyword(s):

American West ◽

Large Scale ◽

Sea Surface ◽

System Model ◽

Drought Risk ◽

Last Millennium ◽

Atmospheric Variability ◽

The Past ◽

Small Influence ◽

Community Earth System Model

The American West exemplifies drought-sensitive regions with growing populations. Paleoclimate investigations have documented severe droughts in this region before European settling, with major implications for water management and planning. Here, we leverage paleoclimate data assimilation to reconstruct past climate states, enabling a large-scale multivariate investigation of U.S. drought dynamics over the last millennium. These results confirm that La Niña conditions significantly influence southwest U.S. drought over the past millennium but only account for, by one metric, ~13% of interannual drought variability in that region. Atlantic sea surface temperatures may also contribute a small influence, but unexplained variability suggests a substantial role for internal atmospheric variability. This conclusion is buttressed by analysis of simulations from the Community Earth System Model Last Millennium Ensemble. While greenhouse gases will increase future drought risk, as shown in other work, interannual U.S. drought variations will also be widely influenced by processes internal to the atmosphere.

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Thirty thousand years of vegetation development and climate change in Angola (Ocean Drilling Program Site 1078)

Climate of the Past ◽

10.5194/cp-4-107-2008 ◽

2008 ◽

Vol 4 (2) ◽

pp. 107-124 ◽

Cited By ~ 36

Author(s):

L. M. Dupont ◽

H. Behling ◽

J.-H. Kim

Keyword(s):

Rain Forest ◽

Vegetation History ◽

First Record ◽

Dry Forest ◽

Sea Surface ◽

Sea Surface Temperatures ◽

Miombo Woodlands ◽

Vegetation Development ◽

The Past ◽

Surface Temperatures

Abstract. ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1, a northward excursion of the Angola Benguela Front and the Congo Air Boundary resulted in cool sea surface temperatures but rain forest remained present in the northern lowlands of Angola. Rain forest and dry forest area increase 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant.

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Late Pliocene Cordilleran Ice Sheet development with warm northeast Pacific sea surface temperatures

Climate of the Past ◽

10.5194/cp-16-299-2020 ◽

2020 ◽

Vol 16 (1) ◽

pp. 299-313 ◽

Cited By ~ 2

Author(s):

Maria Luisa Sánchez-Montes ◽

Erin L. McClymont ◽

Jeremy M. Lloyd ◽

Juliane Müller ◽

Ellen A. Cowan ◽

...

Keyword(s):

Ocean Circulation ◽

Ice Sheet ◽

Gulf Of Alaska ◽

Sea Surface ◽

Early Pleistocene ◽

Late Pliocene ◽

Subarctic Pacific ◽

Cordilleran Ice Sheet ◽

Forcing Mechanisms ◽

Atmospheric Co2 Concentrations

Abstract. The initiation and evolution of the Cordilleran Ice Sheet are relatively poorly constrained. International Ocean Discovery Program (IODP) Expedition 341 recovered marine sediments at Site U1417 in the Gulf of Alaska (GOA). Here we present alkenone-derived sea surface temperature (SST) analyses alongside ice-rafted debris (IRD), terrigenous, and marine organic matter inputs to the GOA through the late Pliocene and early Pleistocene. The first IRD contribution from tidewater glaciers in southwest Alaska is recorded at 2.9 Ma, indicating that the Cordilleran Ice Sheet extent increased in the late Pliocene. A higher occurrence of IRD and higher sedimentation rates in the GOA during the early Pleistocene, at 2.5 Ma, occur in synchrony with SSTs warming on the order of 1 ∘C relative to the Pliocene. All records show a high degree of variability in the early Pleistocene, indicating highly efficient ocean–climate–ice interactions through warm SST–ocean evaporation–orographic precipitation–ice growth mechanisms. A climatic shift towards ocean circulation in the subarctic Pacific similar to the pattern observed during negative Pacific Decadal Oscillation (PDO) conditions today occurs with the development of more extensive Cordilleran glaciation and may have played a role through increased moisture supply to the subarctic Pacific. The drop in atmospheric CO2 concentrations since 2.8 Ma is suggested as one of the main forcing mechanisms driving the Cordilleran glaciation.

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