Factors controlling fluxes and coastal aquatic storage of carbon at the superhumid continental margin of the southern Andes
Final Report Abstract
After the Late Glacial ice retreat from most areas of the Patagonian Andes globally important carbon fluxes and sinks developed in the newly established fjord system, whereas the bioproductivity and carbon storage dropped in the open Pacific Ocean at that time. The newly formed carbon sinks at the continental margin of South America also include terrestrial peatland and peaty soils as well as lake and fjord sediments which have been investigated in the context of this project in a WE transect at latitude 52°S across the continental margin of the southernmost Andes. To evaluate the influence of climate and environmental factors on the Late Glacial and Holocene carbon budgets, open sea as well as fjord surface temperatures have been reconstructed by means of alkenone paleotemperature records. Precipitation changes have been deduced from multiproxy stalagmite and sediment records. Additionally, two new pollen records have been analyzed from the hyperhumid area of the transect with the aim to better understand the influence of distinct plant communities and successions concerning the accumulation of terrestrial Corg in sediments. An ongoing monitoring of meteorology, the thermohaline structure of the fjords and run off has also been performed in the working area. First in-situ measurements of the bioproductivity at 14 sites along the fjord transect underline the importance of thin layers with a strongly enhanced bioproductivity and show their formation conditions. Late Glacial to Holocene sediment cores investigated at 13 sites along the fjord traverse show a strong dependence of the biogenic carbonate accumulation (5 to 20 kg C/m2/kyr) on the degree of progressive marine transgression. These accumulation rates were partly reduced by surface water freshening during very humid periods and during colder Neoglacial periods, in particular during the 1.5°C lower SST’s during the Little Ice Age. In many lake and fjord sediment cores form the hyperhumid central and western area of the transect the total Corg contents range from 5 to >30 wt% whereas Eastern fjord sites (OTW, SKY1 and MD3132) which are related to low precipitation (<500 mm/year) and a steppe vegetation have less than 5 wt.% C org. The contribution from aquatic and terrestrial sources in the fjord sediments has been calculated by welldefined N/C ratios of both endmembers. The records of the marine/aquatic Corg accumulation rates (up to 22 kg/m2/kyr) indicate that the related bioproductivity was less sensitive to changes in surface water Salinities and that algae growth was likely more enhanced during periods with a stronger chemical weathe-ring and micronutrient supply. Sediments from the hyperhumid western island zone and the central fjords which are surrounded by a dense rainfall forest and peaty soils (MDD, CHURR, TM1, TML1) have accumulated up to 55 kg terrestrial Corg/m2/kyr. Particularly humid periods in the Holocene periods the terrestrial Corg is accumulation up to 3-fold higher than the aquatic Corg accumulation. Peat records have been analyzed with respect to changes in Holocene accumulation as well as decomposition rates and its controlling factors. Corg accumulation rates are highest in Sphagnum dominated ombrogenic environments of the late Holocene. Peat decomposition rates are predominately influenced by the development from minerogenic to ombrogenic peat bogs and the overall plant succession, but only to a minor extend by precipitation and temperature changes. Decomposition rates are remarkably higher after deposition of volcanic tephras. Cave stalagmites and hydrological studies from the hyperhumid area of the transect show that higher precipitation let to lower DOC contents and associated metal transport in most run off water, whereas the release of DOC and dissolved metals in five different peat-bearing catchments on the semiarid eastern slopes of the Andes and the Patagonian steppe, shows a strong increase with precipitation. The Patagonian fjords cover an area of 240000 km2. If we consider only half of the area as appropriate for significant accumulation of carbon-bearing sediment our data compilation suggest a Late Glacial and Holocene carbon burial of about 70 GT C. This represents about 5% of global long-term carbon storage in oceanic sediments during that time and is 3-times higher than all Patagonian peat land carbon storage (18 GT C).
Publications
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(2011): Millennial-scale sea surface temperature and Patagonian Ice Sheet changes off southernmost Chile (53°S) over the past 60 kyr. Paleoceanography, 26(3): PA3221
Caniupán, M., Lamy, F., Lange, C., Kaiser, J., Arz, H., Kilian, R., Baeza, O., Aracena, C., Hebbeln, D., Kissel, C., Laj, C. & Mollenhauer, G.
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(2012): A review of Glacial and Holocene paleoclimate records from southernmost Patagonia (49-55°S). Quaternary Science Reviews, 53: 1-23
Kilian, R., & Lamy, F.
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(2012): Peat decomposition records in three pristine ombrotrophic bogs in southern Patagonia. Biogeosciences 9, 1479–1491
Broder, T., Blodau, C., Biester, H. & Knorr, K. H.
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(2013): A 17,300-year record of mercury accumulation in a pristine lake in southern Chile. Journal of Paleolimnology, 49: 547–561
Hermanns, Y.-M. & Biester, H.
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(2013): Late Glacial and Holocene peleogeographical and paleoecological evolution of the seno Skyring and Otway fjord systems in the Magellan region. Anales del Inst. Patagonia, 41 (2): 7-21
Kilian, R., Baeza, O., Breuer, S., Ríos, F., Arz, H.W., Lamy, W., Wirtz, J., Baque, D., Korf, P., Kremer, K., Ríos, C., Mutschke, E., Simon, M., De Pol-Holz, R., Arevalo, M., Wörner, G., Schneider, C. & Casassa G.
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(2013): Late Quaternary variations of the southern westerly wind belt and its influences on aquatic ecosystems and glacier extend within the southernmost Andes. Z. Dt. Ges. Geowiss, 164 (2): 279-294
Kilian, R., Lamy, F. & Arz H.W.
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(2013): Untangling the influence of inlake productivity and terrestrial organic matter flux on 4,250 years of mercury accumulation in Lake Hambre, Southern Chile. Journal of Paleolimnology, 49: 563–573
Hermanns, Y.-M., Cortizas, A. M., Arz, H., Stein, R. & Biester, H.
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(2014): Holocene sea-surface temperature variability in the Chilean fjord region. Quaternary Research, 82: 342-353
Caniupán, M.,· Lamy, F., Lange, C.B., Kaiser, J., Kilian, R., Arz, H.W., León, T., Mollenhauer, G., Sandoval, S., DeHolz, R., Pantoja, S., Wellner, J. & Tiedemann, R.
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(2015). Holocene denudation rates from the southernmost Chilean Patagonian Andes (53°S) deduced from lake sediment budgets. Geomorphology, 187: 135–152
Breuer, S., Kilian, R., Baeza, O., Lamy, F., Arz, H.
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(2015): Holocene variations in productivity associated with changes in glacier activity and freshwater flux in the central basin of the Strait of Magellan. Palaeogeography Palaeoclimatology Palaeoecology, 436: 112-122
Aracena, C., Kilian, R., Lange, C.B., Bertrand, S., Lamy, F., Arz, H.W., De Pol-Holz, R., Baeza, B., Pantoja, S. & Kissel, C.
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(2015): Isoprenoid and branched GDGT-based proxies for surface sediments from marine, fjord and lake environments in Chile. Organic Geochemistry, 89
Kaiser, J., Schouten, S., Kilian, R., Arz, H., Lamy, F., Sinninghe Damsté, J.S.
