Tonu Martma - Academia.edu (original) (raw)

Papers by Tonu Martma

Isotopes in Environmental and Health Studies, 2016

A new data set of δ(2)H and δ(18)O in the groundwater from the central part of the Baltic Artesia... more A new data set of δ(2)H and δ(18)O in the groundwater from the central part of the Baltic Artesian Basin is presented. The hydrogeological section is subdivided into stagnation, slow exchange and active exchange zones. Na-Ca-Cl brine found at the deepest part - the stagnation zone - is characterized by δ(18)O values above -5 ‰ and δ(2)H values approaching -40 ‰ with respect to Vienna Standard Mean Ocean Water. The slow exchange zone where waters of mostly intermediate salinity reside is characterized by δ(18)O values around -11.7 ‰ and δ(2)H values around -85.3 ‰. Mean δ(18)O and δ(2)H values of the fresh groundwater in the active water exchange zone are -11.1 and -79.9 ‰, respectively. Characteristically, the groundwater in the active and slow exchange zone is isotopically more depleted compared with the precipitation values observed, and the depletion increases with depth down to the level where strongly enriched brines are encountered.

Limnology and Oceanography, 2013

The grazing impact of different sized zooplankton on 'edible' and total phytoplankton biomass and... more The grazing impact of different sized zooplankton on 'edible' and total phytoplankton biomass and primary production was measured in L. Võ rtsjä rv during a seasonal study in 1998 and 2000. The organisms of 48-100 lm size class, composed of ciliates and rotifers, contributed significantly to the total grazing of zooplankton community throughout the study period (average 68%). The average daily filtering and grazing rate of the whole zooplankton community (micro-and macro-zooplankton) remained low, corresponding to a filtration of 44% of the water volume, 4% of the total phytoplankton biomass and 29% of primary production. However, a strong grazing pressure on small-sized phytoplankton (<30 lm) was estimated in most of the study period (average 44% d -1 ). Among size classes of 'edible' phytoplankton, the size range 5-15 lm was the most important algal food for the dominant zooplankton grazers (herbivorous ciliates, Polyarthra spp., Chydorus sphaericus and Daphnia cucullata) in L. Võ rtsjä rv.

Nature communications, Jan 11, 2016

Gas hydrates stored on continental shelves are susceptible to dissociation triggered by environme... more Gas hydrates stored on continental shelves are susceptible to dissociation triggered by environmental changes. Knowledge of the timescales of gas hydrate dissociation and subsequent methane release are critical in understanding the impact of marine gas hydrates on the ocean-atmosphere system. Here we report a methane efflux chronology from five sites, at depths of 220-400 m, in the southwest Barents and Norwegian seas where grounded ice sheets led to thickening of the gas hydrate stability zone during the last glaciation. The onset of methane release was coincident with deglaciation-induced pressure release and thinning of the hydrate stability zone. Methane efflux continued for 7-10 kyr, tracking hydrate stability changes controlled by relative sea-level rise, bottom water warming and fluid pathway evolution in response to changing stress fields. The protracted nature of seafloor methane emissions probably attenuated the impact of hydrate dissociation on the climate system.

For a long time, lakes were considered unimportant in the global carbon (C) cycle because of thei... more For a long time, lakes were considered unimportant in the global carbon (C) cycle because of their small total area compared to the ocean. Over the last two decades, a number of studies have highlighted the important role of lakes in both sequestering atmospheric C and modifying the C flux from the catchment by degassing CO2 and methane and burying calcite and organic matter in the sediment. Based on a full C mass balance, high frequency
measurements of lake metabolismand stable isotope analysis of a large shalloweutrophic lake in Estonia, we assess the role alkaline lakes play in augmenting the strength of terrestrial carbonate weathering as a temporary CO2 sink. We show that a large part of organic C buried in the sediments in this type of lakes originates from the catchment although a direct uptake from the atmosphere during periods of intensive phytoplankton growth in eutrophic conditions contributes to the carbon sink.

Isotopes in Environmental and Health Studies, 2015

The unsaturated zone is an important part of the water cycle, governed by many hydrological and h... more The unsaturated zone is an important part of the water cycle, governed by many hydrological and hydrogeological factors and processes and provide water and nutrients to the terrestrial ecosystem. Besides, the soils of the unsaturated zone are regarded as the first natural barrier to a large extent and are able to limit the spread of contaminants depending on their properties. The unsaturated zone provides a linkage between atmospheric moisture, groundwater, and seepage of groundwater to streams, lakes, or other surface water bodies. The major difference between water flow in saturated and unsaturated soils is that the hydraulic conductivity, which is conventionally assumed to be a constant in saturated soils, is a function of the degree of saturation or matrix suction in the unsaturated soils. In Lithuania, low and intermediate level radioactive wastes generated from medicine, industry and research were accumulated at the Maisiagala radioactive waste repository. Short-lived low and intermediate levels radioactive waste, generated during the operation of the Ignalina Nuclear Power Plant (INPP) and arising after the INPP decommissioning will be disposed of in the near surface repository close to the INPP (Stabatiske site). Extensive data sets of the hydraulic properties and water content attributed to unsaturated zone soil profiles of the two radioactive waste disposal sites have been collected and summarized. Globally widespread radionuclide tritium ((3)H) and stable isotope ratio ((18)O/(16)O and (2)H/(1)H) distribution features were determined in precipitation, unsaturated zone soil moisture profiles and groundwater.

Polar Geography and Geology, 1985

First results of isotope‐geochemical investigations of an ice core from Vestfonna (Nordaustlandet... more First results of isotope‐geochemical investigations of an ice core from Vestfonna (Nordaustlandet) are presented. Interpretation of δO and Cl curves is based on data on the stratigraphy of the ice core, according to which the mean annual rate of accumulation is 81 cm w.e. The upper part of the δO curve from the core is in good keeping with data

Polar Geography and Geology, 1986

In order to study the stratification an ice core 208 m in length was extracted from the Vestfonna... more In order to study the stratification an ice core 208 m in length was extracted from the Vestfonna Ice Dome, Nordaustlandet; samples were taken in order to measure total ß‐activity and Cl concentrations. Comparison with the ß‐activity profile with Sr concentrations in atmospheric precipitation made it possible to identify the 1962 accumulation layer at a depth of 24 m. Mean

... STUDY SITE Lake Kahala (59 29T" J, 25 31'E) is located about 40 km east of Tallinn, ... more ... STUDY SITE Lake Kahala (59 29T" J, 25 31'E) is located about 40 km east of Tallinn, near the Tallinn-Narva motorway, at the western corner of the Lahemaa National Park, not far from theklint escarpment ... Additionally, algae can assimilate HCOj as a carbon source (Lucas, 1975 ...

Estonian Journal of Ecology, 2011

In order to assess the geochemical and stable isotopic response of recent sediments to the changi... more In order to assess the geochemical and stable isotopic response of recent sediments to the changing anthropogenic influence on Lake Nõmmejärv, bulk geochemistry determined by XRF spectroscopy and carbon and oxygen stable isotopes in carbonates (δ 13 C carb and δ 18 O carb ) were analysed. A time scale was defined by the 210 Pb dating method. The most significant change in sediment composition was a steep transition from organic to mineral rich sediment at the beginning of the 1970s. Our data confirm that this shift was caused by an abrupt influx of allochthonous mineral matter (Si, Al, K, Rb, Ti, Zr) derived from mine waters that started to be drained from an oil shale mine into the lake through an artificial channel. Since then, the minerogenic sedimentation remains high but after the initial peak, the proportion of siliciclastic matter decreases in favour of CaCO 3 accumulation. During the last 40 years the carbonate content increased from 7% to 40%. Geochemical evidence supports the assumption that the key mechanism in the formation of carbonates was biologically mediated authigenic CaCO 3 precipitation. In addition, decrease in sediment organic matter due to high minerogenic sedimentation forms more favourable conditions for the preservation of the accumulated CaCO 3 . The shift in the δ 13 C carb values during the 1970s and 1980s indicates potential links between CaCO 3 precipitation and the increase in lake productivity.

... N arin R. T arim R. Balkhash Lake Issik Kul Lake Pobeda - Khan Tengry Massif 0 20 10 30 km N ... more ... N arin R. T arim R. Balkhash Lake Issik Kul Lake Pobeda - Khan Tengry Massif 0 20 10 30 km N Page 6. ... The equilibration technique was used for preparation of samples [Epstein and Mayeda, 1953]. Precision of the data was ±0.1 per mil for oxygen and 2 per mil for hydrogen. ...

The Upper Ordovician Boda Limestone and the unconformably overlying Glisstjärn Formation in the S... more The Upper Ordovician Boda Limestone and the unconformably overlying Glisstjärn Formation in the Siljan district, Sweden, were sampled for carbon isotope analysis. The aim is to combine chemo-andAbsolutely final meeting of IGCP 503: Ordovician ...

Annals of Glaciology, 2002

Geological Magazine, 1999

Abstract An episode of remarkable biotic, climatic, sea-level and facies changes took place durin... more Abstract An episode of remarkable biotic, climatic, sea-level and facies changes took place during the late Viruan (Caradoc) epoch in the Baltoscandian area. We studied the carbon isotopic composition of carbonate sediments from this period. Data on the stable carbon ...

Egs Agu Eug Joint Assembly, 2003

Positive carbon isotope excursions (ca 1.5 permil) occur in North American and East European carb... more Positive carbon isotope excursions (ca 1.5 permil) occur in North American and East European carbonates of Late Ordovician (Caradocian) age. However, bulk organic carbon isotope records in three North American localities (Iowa, Ontario and Pennsylvania) and one Estonian locality indicate that carbon isotope fractionation by marine photoautotrophs decreased during this event. Such a decrease is unexpected. During other parts of Earth history, carbon isotope excursions, typically ascribed to organic carbon burial events, are commonly associated with a decrease in carbon isotope fractionation. However, at predicted Ordovician pCO2 and O2 concentrations, marine photosynthesis is not expected to be carbon-limited and carbon isotope fractionation will be constant despite the inferred pCO2 decrease. To further evaluate whether this represents evidence for relatively lower pCO2 levels (<8 times modern pre-industrial level) than those predicted by geochemical models, we deconstructed the organic carbon isotopic records using compound-specific carbon isotope analysis. The most dramatic increase in bulk organic carbon isotopic compositions (8 permil) occurs in the Iowa Guttenberg Formation, while a 5 permil increase occurs in sediments from Southern Ontario. In both cases, the carbon isotope excursion is associated with a change in organic matter assemblage: from a predominance of amorphous, presumably algal and bacterial, marine organic matter to abundant remains of the organic-walled microfossil Gloeocapsomporpha prisca. Biomarker analyses reveal that this shift in organic matter assemblage has strongly influenced the bulk organic carbon isotope record, and biomarkers (steranes, high-molecular-weight n-alkanes) that do not derive from G. prisca exhibit only a 3 to 4 permil excursions, consistent with the bulk organic records from Pennsylvania and Estonia. However, even biomarker-based calculations indicate that carbon isotope fractionation decreased during the isotope event, consistent with a dramatic decrease in pCO2. Alternatively, doubling of phytoplankton growth rates could also account for the observed decrease. An increase in productivity, and thus growth rate, is consistent with proposed changes in ocean circulation and sedimentological evidence for an increase in terrigenous inputs. Moreover, dramatic changes in the distributions of algal and bacterial biomarkers in the Iowa section provide evidence for a change in oceanographic conditions associated with the event. In particular, a dramatic decrease in the abundance of cyanobacterial biomarkers across the boundary suggests that nitrate-limiting conditions could have prevailed prior to the carbon isotope excursion but ceased at that point due to increased nutrient inputs. If so, the productivity event must have been regionally widespread, potentially recording a significant input of terrigenous nutrients into marine settings during the Taconic orogeny.