This thesis is missing page 57, this page is not in any of the other copies. -Digitization Centre / Scientists believe that the global climate is undergoing significant changes due to anthropogenic increases of carbon dioxide (CO2) and other Greenhouse gases. The relationship between climate and vegetation is not fully understood. Knowledge of the response of vegetation to past climate change aids in the understanding of potential vegetation responses to climatic changes due to the Greenhouse effect. The objectives of this thesis were to determine if vegetation in the lower Lena River Region has changed in the past, what were the factors which caused the changes and over what time scales did the changes occur. To address the objectives, the pollen, stomate and sediment stratigraphy of a core from a medium size lake, located in north-central Siberia, were analysed. Radiocarbon dating indicates that the record spans the last 12310 yr BP, and possibly the last 15000 yr BP. The early part of the fossil record was characterised by short rapid changes in the vegetation. The initial shrub tundra was quickly replaced by herb tundra with sparse vegetation cover. This was followed by a reversion to shrub tundra conditions at ~12000 yr BP. A clear Younger Dryas signal is found in this record between 11000 and 10000 yr BP, characterised by a shift from shrub tundra to herb tundra dominated by taxa with arctic affinities. The warming at the close of the Younger Dryas signalled the first appreciable climatic amelioration at this site. Following 10000 yr BP, Alnus became abundant in the pollen record and likely on the landscape. The dominance of Alnus was short lived however. At ~8500 yr BP arboreal vegetation, dominated by Larix dahurica, became abundant in the pollen and stomate record. The expansion of forests was the result of changes in the orbital parameters of the earth as predicted by Milankovitch cycles. Arboreal vegetation persisted in this region until-3500 yr BP when the modem shrub tundra vegetation was established. The use of a new technique, stomate analysis, proved extremely useful. Stomates accurately recorded the expansion and retreat of treeline across this region. This study clearly indicates the usefulness of this technique, especially for investigating fluctuations of treeline. / Thesis / Master of Science (MS)

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Environmental Sciences." Includes bibliographical references (p. 106-112).

The amount of organic carbon (OC) present in Siberian Arctic permafrost soils is estimated at twice the amount of carbon currently in the atmosphere. The shelf seas of the Arctic Ocean receive large amounts of this terrestrial OC from Eurasian Arctic rivers and from coastal erosion. Degradation of this land-derived material in the sea would result in the production of dissolved carbon dioxide and may then add to the atmospheric carbon dioxide reservoir. Observations from the Siberian Arctic suggest that transfer of carbon from land to the marine environment is accelerating. However, it is not clear how much of the transported OC is degraded and oxidized, nor how much is removed from the active carbon cycle by burial in marine sediment. Using bulk geochemical parameters, total OC, d13C and D14C isotope composition, and specific molecular markers of plant wax lipids and lignin phenols, the abundance and composition of OC was determined in both dissolved and particulate carrier phases: the colloidal OC (COC; part of the dissolved OC), particulate OC (POC), and sedimentary OC (SOC). Statistical modelling was used to quantify the relative contribution of OC sources to these phases. Terrestrial OC is derived from the seasonally thawing top layer of permafrost soil (topsoil OC) and frozen OC derived from beneath the active layer eroded at the coast, commonly identified as yedoma ice complex deposit OC (yedoma ICD-OC). These carbon pools are transported differently in the aquatic conduits. Topsoil OC was found in young DOC and POC, in the river water, and the shelf water column, suggesting long-distance transport of this fraction. The yedoma ICD-OC was found as old particulate OC that settles out rapidly to the underlying sediment and is laterally transported across the shelf, likely dispersed by bottom nepheloid layer transport or via ice rafting. These two modes of OC transport resulted in different degradation states of topsoil OC and yedoma ICD-OC. Terrestrial CuO oxidation derived biomarkers indicated a highly degraded component in the COC. In contrast, the terrestrial component of the SOC was much less degraded. In line with earlier suggestions the mineral component in yedoma ICD functions as weight and surface protection of the associated OC, which led to burial in the sediment, and limited OC degradation. The degradability of the terrestrial OC in shelf sediment was also addressed in direct incubation studies. Molecular markers indicate marine OC (from primary production) was more readily degraded than terrestrial OC. Degradation was also faster in sediment from the East Siberian Sea, where the marine contribution was higher compared to the Laptev Sea. Although terrestrial carbon in the sediment was degraded slower, the terrestrial component also contributed to carbon dioxide formation in the incubations of marine sediment. These results contribute to our understanding of the marine fate of land-derived OC from the Siberian Arctic. The mobilization of topsoil OC is expected to grow in magnitude with climate warming and associated active layer deepening. This translocated topsoil OC component was found to be highly degraded, which suggests degradation during transport and a possible contribution to atmospheric carbon dioxide. Similarly, the yedoma ICD-OC (and or old mineral soil carbon) may become a stronger source with accelerated warming, but slow degradation may limit its impact on active carbon cycling in the Siberian Shelf Seas. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

Arctic rivers transport 31-42 Tg organic carbon (OC) each year to the Arctic Ocean, which is equal to 10% of the global riverine OC discharge. Since the Arctic Ocean only holds approximately 1% of the global ocean volume, the influence of terrestrially derived organic carbon (OCter) in the Arctic Ocean is relatively high. Despite the global importance of this region the behavior of the, by far largest fraction of the OCter, the dissolved organic carbon (DOC) in Arctic and sub-arctic estuaries is still a matter of debate. This thesis describes data originating from field cruises in Arctic and sub-arctic estuaries and coastal areas with the aim to improve the understanding of the fate of OCter in these areas, with specific focus on DOC. All presented studies indicate that DOCter and terrestrially derived particulate organic carbon (POCter) are subjected to substantial degradation in high-latitude estuaries, as shown by the non-conservative behavior of DOC in the East Siberian Arctic Shelf Seas (ESAS) (paper I) and the even more rapid degradation of POC in the same region (paper II). The removals of OCter in Arctic shelf seas were further supported by multiple isotope studies (paper III and IV), which showed that a use of 13C/12C in both OC and DIC, together with 34S/32S is a powerful tool to describe the sources and fate of OCter in estuaries and coastal seas. High-latitude estuaries play a key role in the coupling between terrestrial and marine carbon pools. In contrast to the general perception, this thesis shows that they are not only transportation areas for DOCter from rivers to the ocean, but are also active sites for transformation, degradation and sedimentation of DOCter, as well as for POCter. In a rapidly changing climate, the importance of these areas for the coupling between inorganic and organic carbon pools cannot be underestimated. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 2: Submitted. Paper 4: Manuscript.</p>