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In this dissertation, I explore elements of the changing Arctic Ocean through the application of Stable Isotope, Noble Gas Isotopes, and sulfur hexafluoride (SF6) to better understand ice dynamics for freshwater balance, air/sea gas exchange and ocean circulation. For the tracer studies of stable isotope fractionation, our approach is to use sea ice core data to determine the stable oxygen isotope effective fractionation coefficient. The result is an average value close to 2.2 ‰, which is compared to literature values. For the tracer studies of air/sea gas exchange, we use Neon (Ne) and Helium (He) isotope data sets collected in the ‘Switchyard’ region of the Arctic Ocean between 2005 and 2013 and in the Greenland and Norwegian seas between 1994 and 1999. The Switchyard data show a distinct excess in Ne concentrations in the upper waters. We hypothesize that rejection of Ne during sea ice formation accounts for the Ne excess in the Switchyard area of the Arctic Ocean. Based on this hypothesis we estimate sea-ice formation rates by integrating the Ne excess from the surface to the Atlantic Water layer. The resulting amount of excess Ne corresponds to formation of a nearly 4 m thick sea ice layer. We compare the sea ice formation obtained from the Ne excess method with an independent estimate based on oxygen isotope ratio anomalies ?18O, which is nearly 6.07 m. The difference in the sea ice formation estimated by these two methods indicates loss of Ne through leads. We estimate that the gas exchange rate through the sea-ice cover is ca. 11.3 percent per year. The gas exchange rate through sea-ice covered water would be 0.015 meters per day. For the tracer studies of mean residence times, we analyzed tritium (3H), helium isotope (3He and 4He) and sulfur hexafluoride (SF6) samples collected in the ‘Switchyard’ region of the Arctic Ocean between 2008 and 2013. We calculated apparent tracer ages using the 3H/3He ratios and the partial pressure of SF6 and compare their values for the depth interval between the surface and the core of the Atlantic Water layer. The apparent tracer ages range from zero to about 30 years. Generally, the linear correlation between the 3H/3He and SF6 apparent ages was strong, with the coefficient of determination R2 of 0.94. We explore deviations from this linear trend and discuss them in the context of mixing, air-sea gas exchange, and the impact of sea ice formation on the helium and SF6 gas balances in the surface mixed layer.

Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake. At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species. Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Several areas in Namaqualand are affected by elevated levels of salinity; including the shallow alluvial aquifers along the Buffels River catchment. The chemistry of rainwater that recharges these aquifers has low salt-loads, but the groundwater system is very saline. The shallow alluvial aquifers are an important source of water for several communal areas along the river both for domestic and agricultural purposes. Groundwater is also used for the copper and diamond mining activities along the river. Prior to this study, the sources of salinity to the alluvial aquifers and whether salinity can be remediated has not been determined. Possible salinity sources included seawater intrusion, evaporitic salts dissolution, concentrations by evaporation, deep aquifer brines, dissolution of minerals from the aquifer geology as well as salts from anthropogenic activities (i.e. mining). The source(s) of salinity to the groundwater has been determined using the geochemical as well as the isotopic tracers. The ratios of major ions (i.e. Na/Cl) as well the oxygen (18O), hydrogen (2H), 36Cl/Cl, and 87Sr/86Sr isotopes were used in determining the possible solute sources. In addition to these, the chloride mass balance (CMB) method was used to determine the recharge rates to the alluvial aquifers. Furthermore, the groundwater age of the alluvial aquifers was determined using the tritium (3H) isotope. The groundwater samples have high 87Sr/86Sr ratios, which are in the same ranges as the 87Sr/86Sr ratios in the surrounding granitic rocks indicating water-rock interactions. The 36Cl/Cl ratios are low and indicate the dissolution of old salts. The 18O and 2H stable isotopes of groundwater show an evaporative trend with respect to the LMWL, which indicate that groundwater has been evaporated before or during infiltration. Salinity to the shallow alluvial aquifers was found to be mainly derived from the dissolution of rock mass and concentration by evaporation process. The groundwater is relatively young, but there is mixing between old water recharged prior to bomb testing and recently recharged groundwater in some boreholes. The Chloride mass balance (CMB) method assumes atmospheric chloride is the only source of chloride to the aquifers. However, there is additional chloride to these alluvial aquifers from rock mass dissolution. The estimated recharge rates by CMB method (0.1-3.4mm/a) are therefore underestimated. A simulation model was used to determine the recharge rates based on the annual precipitation that will yield the current measured chloride concentrations in the groundwater. Recharge was found to range from 1-5% of the annual precipitation, which is also low. The CMB method therefore gives significant recharge rate estimates, but they are not accurate and need to be supported by another method. / AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.

<p>Obesity is a major health problem in the Western world. Mean birth weight has increased during the last 25 years. One explanation is that the proportion of large for gestational age (LGA) infants has increased. Such infants risk developing obesity, cardiovascular disease and diabetes later in life. Despite the risk of neonatal hypoglycemia, their postnatal metabolic adaptation has not been investigated. Our data, obtained with stable isotope labeled compounds, demonstrate that newborn LGA infants have increased lipolysis and decreased insulin sensitivity. After administration of glucagon, the plasma levels of glucose and the rate of glucose production increased. The simultaneous increase in insulin correlated with the decrease in lipolysis, indicating an antilipolytic effect of insulin in these infants.</p><p>We also demonstrated an intergenerational effect of being born LGA, since women born LGA, were at higher risk of giving birth to LGA infants than women not born LGA. Further, the LGA infants formed three subgroups: born long only, born heavy only, and born both long and heavy. Infants born LGA of women with high birth weight or adult obesity were at higher risk of being LGA concerning weight alone, predisposing to overweight and obesity at childbearing age. In addition we found that pregnant women with gestational diabetes were at increased risk of giving birth to infants that were heavy alone. This could explain the risk of both perinatal complications and later metabolic disease in infants of this group of women.</p><p>To identify determinants of fetal growth, 20 pregnant women with a wide range of fetal weights were investigated at 36 weeks of gestation. Maternal fat mass was strongly associated with insulin resistance. Insulin resistance was related to glucose production, which correlated positively with fetal size. The variation in resting energy expenditure, which was closely related to fetal weight, was largely explained by BMI, insulin resistance, and glucose production. Lipolysis was not rate limiting for fetal growth in this group of women. Consequently, high maternal glucose production due to a high fat mass may result in excessive fetal growth.</p>

<p>This paper deals with the late Viking age/early medieval grave field in Björned, Torsåker parish, Ångermanland County in northern Sweden. The grave field in Björned is rare because it has all the signs of being Christianized before the surroundings. This awakes questions such as if the people of Björned came from another place and brought the religion with them or if someone else did that for them. To find these answers I have analysed the stable isotope ratios [delta]13C, [delta]15N and [delta]34S in human bone collagen. Through these stable isotopes we can not only see what the people consumed but also where their food had its origin. It seems like several people from the grave field had a different origin then the rest.</p>

<p>This paper deals with diet and gender in the early roman iron age in Sweden. Human bone and tooth material from the Iron Age cemetery at Bjärby in Kastlösa parish on the island of Öland have been analysed for stable carbon and nitrogen isotopes. 21 individuals were sampled. Where possible 4 samples were taken from each individual, from the first, second and third molar respectively and from one compact bone. By doing so it is possible, at least in theory, to trace intra-individual diets throughout life. In total, 64 samples were analysed by isotope ratio mass spectrometer. The low [delta]13C values indicate a diet based mostly on terrestrial resources, while the high [delta]15N values indicate some significant marine input. This discrepancy may be explained by an intake of freshwater fish or meat from suckling animals. The isotope values do not indicate any significant dietary reliance on cereals. Some gender differences in diet were observed. The [delta]15N values of the women were higher than those of the men, indicating a higher tropic level throughout life. The third molar [delta]13C values of the men were higher than those of the women, indicating a somewhat more substantial marine input during the teenage years.</p>

During the Late Pliocene, between 3.3 Ma and 2.6 Ma, tectonic events changed ocean basin interactions against a background of shifting orbital forcing mechanisms and a global cooling trend. A climate system that had been locked in a stable, warm state gradually transformed into one typified by the high-amplitude glacial–interglacial fluctuations characteristic of the later Quaternary. The onset of Northern Hemisphere glaciations in the Late Pliocene marks an important step in this transition, due to the role of feedback mechanisms including ice albedo. A crucial factor in this Northern Hemisphere ice sheet expansion is the North Atlantic surface ocean circulation. To evaluate how they are linked, a ca. 200-kyr time slab spanning 2782-2520 ka (Late Pliocene–Early Pleistocene) was analyzed at millennial scale resolution from eastern North Atlantic Deep Sea Drilling Project (DSDP) Site 610 and Integrated Ocean Drilling Program (IODP) Site U1313. The causes of the Plio-Pleistocene climatic turnover are compared to that of the well-documented Marine Isotope Stage (MIS) M2 occurring in the Late Pliocene (3.3 Ma). MIS M2, a severe glacial event seen as a precursor to later Quaternary-style glaciations, was investigated from western North Atlantic DSDP Site 603. Utilizing a same-sample methodology, two paleoceanographic proxies were used: (1) dinocyst assemblages, and (2) foraminiferal geochemistry (δ18O and Mg/Ca). Dinocysts are proven tracers of sea-surface temperature (SST), salinity, nutrient supply, and sea ice cover, and are analyzed here to characterize the overlying water masses at the studied sites. Strong dinocyst assemblage fluctuations attest to variations in the influence of the North Atlantic Current (NAC). Using Mg/Ca ratios for the planktonic foraminifer Globigerina bulloides to determine absolute SSTs allows salinity changes to be reconstructed when combined with stable oxygen isotopes. This study shows a persistent Gulf Stream–NAC in the western North Atlantic during MIS M2, favoring a southern shift of the NAC over a shutdown of the thermohaline circulation. At the newly established Plio-Pleistocene boundary, a profound turnover in dinoflagellate cyst assemblages reveals a shift in ocean mode during MIS 104 (2.6 Ma). Three distinct dinocyst ecozones demonstrate this fundamental reorganization of the North Atlantic circulation.

Northern lakes and ponds are abundant and emit large amounts of the potent climate forcer methane to the atmosphere at rates prone to change with amplified Arctic warming. In spite of being important, fluxes from surface waters are not well understood. Long-term measurements are lacking and the dominant and irregular transport mode ebullition (bubbling) is rarely quantified, which complicate the inclusion of lakes and ponds in the global methane budget. This thesis focuses on variations in emissions on both local and regional scales. A synthesis of methane fluxes from almost all studied sites constrains uncertainties and demonstrates that northern lakes and ponds are a dominant source at high latitudes. Per unit area variations in flux magnitudes among different types of water bodies are mainly linked to water depth and type of sediment. When extrapolated, total area is key and thus post-glacial lakes dominate emissions over water bodies formed by peat degradation or thermokarst processes. Further, consistent multiyear measurements in three post-glacial lakes in Stordalen, northern Sweden, reveal that seasonal ebullition, primarily driven by fermentation of acetate, can be predicted by easily measured parameters such as temperature and heat energy input over the ice-free season. Assuming that most water bodies respond similarly to warming, this thesis also suggests that northern lakes and ponds will release substantially more methane before the end of the century, primarily as a result of longer ice-free seasons. Improved uncertainty reductions of both current and future estimates rely on increased knowledge of landscape-level processes related to changes in aquatic systems and organic loading with permafrost thaw, as well as more high-quality measurements, seldom seen in contemporary data. Sampling distributed over entire ice-free seasons and across different depth zones is crucial for accurately quantifying methane emissions from northern lakes and ponds. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>