Sediment core profiles of long-chain n-alkanes in the Sea of Okhotsk: Enhanced transport of terrestrial organic matter from the last deglaciation to the early Holocene

2003 ◽  
Vol 30 (1) ◽  
pp. 1-1-1-4 ◽  
Author(s):  
O. Seki ◽  
K. Kawamura ◽  
T. Nakatsuka ◽  
K. Ohnishi ◽  
M. Ikehara ◽  
...  
2021 ◽  
Author(s):  
Eduardo Queiroz Alves ◽  
Yunyi Wang ◽  
Jens Hefter ◽  
Hendrik Grotheer ◽  
Karin A. F. Zonneveld ◽  
...  

<p>The thawing of permafrost in the polar regions has important implications for climate on Earth. Indeed, permafrost degradation results in a positive climate feedback which is currently aggravated by human action. The dynamic character of Earth’s climate means that past trends and variability can be examined to improve future projections of this effect. Notably, the permafrost zone that covered parts of Europe during the Last Glacial Maximum (LGM) is currently absent, indicating that this region is a crucial area for the study of permafrost carbon remobilization during the last deglacial warming. Here, we investigate the mobilization of permafrost material to the Bay of Biscay, off the English Channel. Although this location has been shown to have experienced an enhanced deposition of terrigenous material during the last deglaciation, the contribution of permafrost thaw is unknown. We have established an accurate and robust chronological framework for this deposition, showing enhanced rates of sediment accumulation from approximately 20.2 to 15.8 kcal BP. Biomarker analysis has revealed periods of marked increases in terrigenous input, namely from approximately 20.5 to 19 and from 19 to 16.5 kcal BP. Moreover, by performing compound specific radiocarbon dating on n-alkanoic acids isolated from the sedimentary archive, we have been able to determine the origin of organic matter deposited at the core location. Our results will help researchers to assess to what extent permafrost thaw contributed to the peak of organic matter deposition present in the marine sediment, allowing us to sharpen our understanding of the mechanisms of permafrost carbon mobilization.</p>


2021 ◽  
Author(s):  
Thomas Extier ◽  
Katharina Six ◽  
Bo Liu ◽  
Tatiana Ilyina

<p>The Last Deglaciation (21-10 ka) is the most recent transition from a glacial to interglacial state. It is characterized by a pronounced sea level change of 95 m resulting in flooding of land areas and changes of coastlines. This period is also marked by several millennial events like the Heinrich Event 1 with diverse effects on sea level, oceanic circulation, climate and carbon cycle. In case of flooding of land surfaces during periods of sea level rise, carbon and nutrients stored in terrestrial organic matter in vegetation and soils are transferred to the ocean, potentially impacting the global ocean biogeochemical cycle and the uptake/release of CO<sub>2</sub> once being remineralized. Changes in the ocean biogeochemical cycles are also indirectly related to the poorly constrained stoichiometry and remineralization time-scales of terrestrial organic matter, which both differ from the well-known parameters for marine organic matter.</p><p>We present here the first coupled transient simulation over the Last Deglaciation using the global ocean biogeochemical model HAMOCC (HAMburg Ocean Carbon Cycle) as part of the paleo-version of the MPI-ESM (Max Planck Institute Earth System Model) to study the impact of terrestrial organic matter input on the ocean biogeochemical cycle and oceanic CO<sub>2</sub> fluxes during large sea level variations. This model version combines (1) a fully interactive adaptation of the ocean bathymetry with corresponding changes of the land-sea distribution, (2) a transient river routing and (3) the land-sea terrestrial organic matter transfer after flooding. Our simulation provides new insights on the land carbon inputs to the ocean carbon inventory (water column and sediment) due to flooding, with 170 GtC between 21-10 ka, of which 21.1 GtC and 36.8 GtC are within two 1000 years large freshwater discharge events (between 15-14 ka and 12-11 ka). These inputs of carbon rich material to the ocean during flooding events have however only a local effect on ocean CO<sub>2</sub> outgassing, the global ocean remaining a sink of CO<sub>2</sub>. To infer the response of CO<sub>2</sub> fluxes in this context, sensitivity experiments can be performed during the type of Heinrich event (15-14 ka) to evaluate and better constrain the terrestrial organic matter remineralization parameters.</p>


2020 ◽  
Author(s):  
Dave Stolwijk ◽  
Marcello Natalicchio ◽  
Francesco Dela Pierre ◽  
Daniel Birgel ◽  
Jörn Peckmann

<p>During the Messinian salinity crisis (MSC), the Mediterranean Sea was gradually isolated from the Atlantic Ocean due to tectonics, ultimately resulting in the deposition of enormous volumes of evaporites on the Mediterranean seafloor. In marginal Mediterranean sub-basins, the first phase of the MSC is represented by a cyclic succession of gypsum and shales (Primary Lower Gypsum unit; PLG), changing laterally into an alternation of shales, marls and carbonates towards the deeper parts of the basins. The current consensus is that the lithological cyclicity is the expression of precession-paced climate oscillations, with shales deposited during insolation maxima (precession minima) and gypsum deposited during insolation minima (precession maxima). However, this hypothesis has yet to be validated, because this assumption is primarily based on the continuation of sedimentary cyclicity from the open marine pre-MSC sediments into the Primary Lower Gypsum unit. To assess the possible role of orbitally-driven paleoclimate change on the deposition of the PLG unit, we have analysed molecular fossils (lipid biomarkers) preserved in shales and gypsum of the Pollenzo section (Piedmont basin, NW Italy).</p><p>Long-chain n-alkanes are reliable biomarkers that are used to track the input of terrestrial organic matter and allow to reconstruct paleovegetation. By using the distribution of higher plant-derived long chain n-alkanes and their compound specific carbon isotope signature (δ<sup>13</sup>C), we show that the sedimentary cyclicity in the PLG unit is indeed controlled by precession. Our high-resolution paleoclimatic proxy records cover approximately 300 Ka (6.003 Ma – 5.721 Ma) and comprise the onset of the MSC (5.971 Ma) and the first 12 cycles of the PLG unit. Cyclic fluctuation of δ<sup>13</sup>C values is observed, with higher δ<sup>13</sup>C values typifying long-chain n-alkanes extracted for gypsum, while lower values correspond to shales.</p><p>Our results, which represent the first paleoclimatic proxy data derived from Messinian gypsum, show that riverine flux of organic matter to the basin varied significantly during the first phase of the MSC. In agreement with a precessional control on paleoclimate, lower n-alkane abundance in gypsum reflects drier conditions, while higher n-alkane abundance in shales indicates more humid climate and increased input of terrestrial organic matter to the basin.</p>


2013 ◽  
Vol 9 (2) ◽  
pp. 767-787 ◽  
Author(s):  
S. Desprat ◽  
N. Combourieu-Nebout ◽  
L. Essallami ◽  
M. A. Sicre ◽  
I. Dormoy ◽  
...  

Abstract. Despite a large number of studies, the long-term and millennial to centennial-scale climatic variability in the Mediterranean region during the last deglaciation and the Holocene is still debated, including in the southern Central Mediterranean. In this paper, we present a new marine pollen sequence (core MD04-2797CQ) from the Siculo-Tunisian Strait documenting the regional vegetation and climatic changes in the southern Central Mediterranean during the last deglaciation and the Holocene. The MD04-2797CQ marine pollen sequence shows that semi-desert plants dominated the vegetal cover in the southern Central Mediterranean between 18.2 and 12.3 ka cal BP, indicating prevailing dry conditions during the deglaciation, even during the Greenland Interstadial (GI)-1. Across the transition Greenland Stadial (GS)-1 – Holocene, Asteraceae-Poaceae steppe became dominant till 10.1 ka cal BP. This record underlines with no chronological ambiguity that even though temperatures increased, deficiency in moisture availability persisted into the early Holocene. Temperate trees and shrubs with heath underbrush or maquis expanded between 10.1 and 6.6 ka, corresponding to Sapropel 1 (S1) interval, while Mediterranean plants only developed from 6.6 ka onwards. These changes in vegetal cover show that the regional climate in southern Central Mediterranean was wetter during S1 and became drier during the mid- to late Holocene. Wetter conditions during S1 were likely due to increased winter precipitation while summers remained dry. We suggest, in agreement with published modeling experiments, that the early Holocene increased melting of the Laurentide Ice Sheet in conjunction with weak winter insolation played a major role in the development of winter precipitation maxima in the Mediterranean region in controlling the strength and position of the North Atlantic storm track. Finally, our data provide evidence for centennial-scale vegetation and climatic changes in the southern Central Mediterranean. During the wet early Holocene, alkenone-derived cooling episodes are synchronous with herbaceous composition changes that indicate muted changes in precipitation. In contrast, enhanced aridity episodes, as detected by strong reduction in trees and shrubs, are recorded during the mid- to late Holocene. We show that the impact of the Holocene cooling events on the Mediterranean hydroclimate depend on baseline climate states, i.e. insolation and ice sheet extent, shaping the response of the mid-latitude atmospheric circulation.


2021 ◽  
Vol 15 (7) ◽  
pp. 3329-3354
Author(s):  
Trevor R. Hillebrand ◽  
John O. Stone ◽  
Michelle Koutnik ◽  
Courtney King ◽  
Howard Conway ◽  
...  

Abstract. Chronologies of glacier deposits in the Transantarctic Mountains provide important constraints on grounding-line retreat during the last deglaciation in the Ross Sea. However, between Beardmore Glacier and Ross Island – a distance of some 600 km – the existing chronologies are generally sparse and far from the modern grounding line, leaving the past dynamics of this vast region largely unconstrained. We present exposure ages of glacial deposits at three locations alongside the Darwin–Hatherton Glacier System – including within 10 km of the modern grounding line – that record several hundred meters of Late Pleistocene to Early Holocene thickening relative to present. As the ice sheet grounding line in the Ross Sea retreated, Hatherton Glacier thinned steadily from about 9 until about 3 ka. Our data are equivocal about the maximum thickness and Mid-Holocene to Early Holocene history at the mouth of Darwin Glacier, allowing for two conflicting deglaciation scenarios: (1) ∼500 m of thinning from 9 to 3 ka, similar to Hatherton Glacier, or (2) ∼950 m of thinning, with a rapid pulse of ∼600 m thinning at around 5 ka. We test these two scenarios using a 1.5-dimensional flowband model, forced by ice thickness changes at the mouth of Darwin Glacier and evaluated by fit to the chronology of deposits at Hatherton Glacier. The constraints from Hatherton Glacier are consistent with the interpretation that the mouth of Darwin Glacier thinned steadily by ∼500 m from 9 to 3 ka. Rapid pulses of thinning at the mouth of Darwin Glacier are ruled out by the data at Hatherton Glacier. This contrasts with some of the available records from the mouths of other outlet glaciers in the Transantarctic Mountains, many of which thinned by hundreds of meters over roughly a 1000-year period in the Early Holocene. The deglaciation histories of Darwin and Hatherton glaciers are best matched by a steady decrease in catchment area through the Holocene, suggesting that Byrd and/or Mulock glaciers may have captured roughly half of the catchment area of Darwin and Hatherton glaciers during the last deglaciation. An ensemble of three-dimensional ice sheet model simulations suggest that Darwin and Hatherton glaciers are strongly buttressed by convergent flow with ice from neighboring Byrd and Mulock glaciers, and by lateral drag past Minna Bluff, which could have led to a pattern of retreat distinct from other glaciers throughout the Transantarctic Mountains.


2005 ◽  
Vol 64 (2) ◽  
pp. 249-256 ◽  
Author(s):  
David A. Vacco ◽  
Peter U. Clark ◽  
Alan C. Mix ◽  
Hai Cheng ◽  
R. Lawrence Edwards

AbstractA well-dated δ18O record in a stalagmite from a cave in the Klamath Mountains, Oregon, with a sampling interval of 50 yr, indicates that the climate of this region cooled essentially synchronously with Younger Dryas climate change elsewhere in the Northern Hemisphere. The δ18O record also indicates significant century-scale temperature variability during the early Holocene. The δ13C record suggests increasing biomass over the cave through the last deglaciation, with century-scale variability but with little detectable response of vegetation to Younger Dryas cooling.


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