Understanding the mechanisms behind high glacial productivity in the southern Brazilian margin

Abstract. This study explores the mechanisms behind the high glacial productivity in the southern Brazilian margin during the last 70 kyr. Therefore, we use planktonic foraminifera assemblage and subsurface temperatures derived through the Modern Analogue Technique. We show that enhanced glacial productivity was driven by the synergy of two mechanisms operating in different seasons: (i) a high productivity upwelling during short austral summer events; and (ii) the persistent presence of the Plata Plume Water due to prolonged austral winter conditions. We suggest that the upwelling systems in the southern Brazilian margin were more productive during the last glacial period due to the enhanced Si supply for diatom production through high-Si thermocline waters preformed in the Southern Ocean. We hypothesize that orbital forcing did not have a major influence on changes in upwelling during the last glacial period. However, the more frequent northward intrusions of the Plata Plume Water were modulated by austral winter insolation at 65 °S through changes in the strength of alongshore SW-winds. After the Last Glacial Maximum, the reduced Si content of thermocline waters decreased upwelling productivity, while lower austral winter insolation decreased the influence of the Plata Plume Water over the southern Brazilian margin, reducing regional productivity.

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Understanding the mechanisms behind high glacial productivity in the southern Brazilian margin

Climate of the Past ◽

10.5194/cp-15-943-2019 ◽

2019 ◽

Vol 15 (3) ◽

pp. 943-955 ◽

Cited By ~ 3

Author(s):

Rodrigo da Costa Portilho-Ramos ◽

Tainã Marcos Lima Pinho ◽

Cristiano Mazur Chiessi ◽

Cátia Fernandes Barbosa

Keyword(s):

Austral Summer ◽

Major Influence ◽

Glacial Period ◽

Austral Winter ◽

Last Glacial Period ◽

Last Glacial ◽

Plume Water ◽

Modern Analogue ◽

Winter Insolation ◽

The Last Glacial

Abstract. This study explores the mechanisms behind the high glacial productivity in the southern Brazilian margin (SBM) during the last 70 kyr using planktonic foraminifera assemblage and subsurface temperature information derived using the modern analogue technique. We show that enhanced glacial productivity was driven by the synergy of two mechanisms operating in different seasons: (i) enhanced productivity in the upwelling region during short austral summer events; and (ii) the persistent presence of the Plata Plume Water (PPW) due to prolonged austral winter conditions. We suggest that the upwelling systems in the southern Brazilian margin were more productive during the last glacial period due to the enhanced Si supply for diatom production by high-Si thermocline waters preformed in the Southern Ocean. We hypothesize that orbital forcing did not have a major influence on changes in upwelling during the last glacial period. However, the more frequent northward intrusions of the Plata Plume Water were modulated by austral winter insolation at 60∘ S via changes in the strength of alongshore southwesterly winds. After the Last Glacial Maximum, the reduced Si content of thermocline waters decreased upwelling productivity, while lower austral winter insolation decreased the influence of the Plata Plume Water over the southern Brazilian margin, reducing regional productivity.

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Alpine permafrost thawing during the Medieval Warm Period identified from cryogenic cave carbonates

The Cryosphere ◽

10.5194/tc-7-1073-2013 ◽

2013 ◽

Vol 7 (4) ◽

pp. 1073-1081 ◽

Cited By ~ 15

Author(s):

M. Luetscher ◽

M. Borreguero ◽

G. E. Moseley ◽

C. Spötl ◽

R. L. Edwards

Keyword(s):

Western Alps ◽

Convincing Evidence ◽

Water Infiltration ◽

Exact Nature ◽

Glacial Period ◽

Calcite Precipitation ◽

Last Glacial Period ◽

Last Glacial ◽

Modern Analogue ◽

The Last Glacial

Abstract. Coarse crystalline cryogenic cave carbonates (CCCcoarse) dated to the last glacial period are common in central European caves and provide convincing evidence of palaeo-permafrost during this time. Little is known, however, about the exact nature of the environment in which CCCcoarse formed as no modern analogue setting is known. Here, we report the first findings of sub-recent, albeit inactive, CCCcoarse from a cave of the Western Alps which is located in the present-day permafrost zone. The globular shape and the presence of ubiquitous euhedral crystal terminations are comparable to previously reported aggregates from the last glacial period and strongly suggest that these aggregates formed subaqueously in pools lacking agitation. Furthermore, stable isotope values of mm-sized spheroids point to calcite precipitation in a closed system with respect to CO2, strongly supporting the hypothesis of a cryogenic origin associated with the freezing of water ponds. U-series analyses revealed three clusters of late Holocene calcite precipitation intervals between 2129 and 751 a b2k. These ages correlate with known periods of elevated summer temperatures, suggesting that warming and thawing of the frozen catchment above the cave allowed water infiltration into the karst system. The growth of CCCcoarse resulted from the re-freezing of this water in the still cold karst cavities.

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Alpine permafrost thawing during the Medieval Warm Period identified from cryogenic cave carbonates

The Cryosphere Discussions ◽

10.5194/tcd-7-419-2013 ◽

2013 ◽

Vol 7 (1) ◽

pp. 419-440

Author(s):

M. Luetscher ◽

M. Borreguero ◽

G. E. Moseley ◽

C. Spötl ◽

R. L. Edwards

Keyword(s):

Western Alps ◽

Convincing Evidence ◽

Water Infiltration ◽

Exact Nature ◽

Glacial Period ◽

Calcite Precipitation ◽

Last Glacial Period ◽

Last Glacial ◽

Modern Analogue ◽

The Last Glacial

Abstract. Coarse crystalline cryogenic cave carbonates (CCCcoarse) dated to the last glacial period are common in central European caves and provide convincing evidence of palaeo-permafrost during this time. Little is known, however, about the exact nature of the environment in which CCCcoarse formed as no modern analogue setting is known. Here, we report the first findings of sub-recent, albeit inactive, CCCcoarse from a cave of the Western Alps which is located in the present-day permafrost zone. The globular shape and the presence of ubiquitous euhedral crystal terminations are comparable to previously described aggregates from the last glacial period and strongly suggest that these aggregates formed subaqueously in pools lacking agitation. Furthermore, stable isotope values of mm-sized spheroids point to calcite precipitation in a closed system with respect to CO2 strongly supporting the hypothesis of a cryogenic origin associated with the freezing of water ponds. U-series analyses revealed three clusters of late Holocene calcite precipitation intervals between 2129 and 751 a b2k. These ages correlate with known periods of elevated summer temperatures, suggesting that warming and thawing of the permafrozen catchment above the cave allowed water infiltration into the karst system. The growth of CCCcoarse resulted from the re-freezing of this water in the still cold karst cavities.

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Insights into continental temperatures in the northwestern Black Sea area during the Last Glacial period using branched tetraether lipids

Quaternary Science Reviews ◽

10.1016/j.quascirev.2013.11.013 ◽

2014 ◽

Vol 84 ◽

pp. 98-108 ◽

Cited By ~ 18

Author(s):

Lise Sanchi ◽

Guillemette Ménot ◽

Edouard Bard

Keyword(s):

Black Sea ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

Tetraether Lipids ◽

Sea Area ◽

The Last Glacial

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Post-depositional manganese mobilization during the last glacial period in sediments of the eastern Clarion-Clipperton Zone, Pacific Ocean

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2019.116012 ◽

2020 ◽

Vol 532 ◽

pp. 116012 ◽

Cited By ~ 2

Author(s):

Jessica B. Volz ◽

Bo Liu ◽

Male Köster ◽

Susann Henkel ◽

Andrea Koschinsky ◽

...

Keyword(s):

Pacific Ocean ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

The Last Glacial

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Modes of eastern equatorial Pacific thermocline variability: Implications for ENSO dynamics over the last glacial period

Paleoceanography ◽

10.1029/2008pa001701 ◽

2009 ◽

Vol 24 (3) ◽

Cited By ~ 59

Author(s):

Guillaume Leduc ◽

Laurence Vidal ◽

Olivier Cartapanis ◽

Edouard Bard

Keyword(s):

Equatorial Pacific ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

Eastern Equatorial Pacific ◽

Enso Dynamics ◽

The Last Glacial ◽

Thermocline Variability

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<i>δ</i><sup>13</sup>C decreases in the upper western South Atlantic during Heinrich Stadials 3 and 2

Climate of the Past ◽

10.5194/cp-13-345-2017 ◽

2017 ◽

Vol 13 (4) ◽

pp. 345-358 ◽

Cited By ~ 4

Author(s):

Marília C. Campos ◽

Cristiano M. Chiessi ◽

Ines Voigt ◽

Alberto R. Piola ◽

Henning Kuhnert ◽

...

Keyword(s):

Climate Change ◽

South Atlantic ◽

Meridional Overturning Circulation ◽

Glacial Period ◽

Last Deglaciation ◽

Last Glacial Period ◽

Last Glacial ◽

Change Events ◽

The Last Glacial ◽

Millennial Scale

Abstract. Abrupt millennial-scale climate change events of the last deglaciation (i.e. Heinrich Stadial 1 and the Younger Dryas) were accompanied by marked increases in atmospheric CO2 (CO2atm) and decreases in its stable carbon isotopic ratios (δ13C), i.e. δ13CO2atm, presumably due to outgassing from the ocean. However, information on the preceding Heinrich Stadials during the last glacial period is scarce. Here we present δ13C records from two species of planktonic foraminifera from the western South Atlantic that reveal major decreases (up to 1 ‰) during Heinrich Stadials 3 and 2. These δ13C decreases are most likely related to millennial-scale periods of weakening of the Atlantic meridional overturning circulation and the consequent increase (decrease) in CO2atm (δ13CO2atm). We hypothesise two mechanisms that could account for the decreases observed in our records, namely strengthening of Southern Ocean deep-water ventilation and weakening of the biological pump. Additionally, we suggest that air–sea gas exchange could have contributed to the observed δ13C decreases. Together with other lines of evidence, our data are consistent with the hypothesis that the CO2 added to the atmosphere during abrupt millennial-scale climate change events of the last glacial period also originated in the ocean and reached the atmosphere by outgassing. The temporal evolution of δ13C during Heinrich Stadials 3 and 2 in our records is characterized by two relative minima separated by a relative maximum. This w structure is also found in North Atlantic and South American records, further suggesting that such a structure is a pervasive feature of Heinrich Stadial 2 and, possibly, also Heinrich Stadial 3.

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