Anne E. Carey

Organic carbon fluxes to the ocean from high-standing islands

The transfer of terrestrially derived (yet poorly quantified) organic carbon to the oceans is an important yet unagreed upon proportion of the worlds carbon budget. The few data that exist suggest that high-standing oceanic islands in the southwest Pacific may make important contributions to the overall terrestrial flux of particulate organic carbon (POC) to the oceans. We have determined the POC flux from several streams in New Zealand. With those data and previous measurements from Taiwan and Papua New Guinea, we estimate the POC flux from high-standing islands in the southwest Pacific to be 48 × 1012 g C yr−1, a value slightly lower than previous estimates. These islands, which make up only ∼3% of Earths landmass, contribute 17%– 35% of the estimated POC entering the worlds oceans annually and thus may be important sources of terrestrial carbon to the ocean. Anthropogenic activities, especially deforestation and forest harvesting, have probably exacerbated the natural flux. Few to no data exist for many of these islands and thus a more detailed assessment awaits further measurements.

Extreme storm events, landscape denudation, and carbon sequestration: Typhoon Mindulle, Choshui River, Taiwan

We have performed the first known semicontinuous monitoring of particulate organic carbon (POC) fluxes and dissolved Si concentrations delivered to the ocean during a typhoon. Sampling of the Choshui River in Taiwan during Typhoon Mindulle in 2004 revealed a POC flux of 5.00 × 105 t associated with a sediment flux of 61 Mt during a 96 h period. The linkage of high amounts of POC with sediment concentrations capable of generating a hyperpycnal plume upon reaching the ocean provides the first known evidence for the rapid delivery and burial of POC from the terrestrial system. These fluxes, when combined with storm-derived CO2 consumption of 1.65 × 108 mol from silicate weathering, elucidate the important role of these tropical cyclone events on small mountainous rivers as a global sink of CO2.

Groundwater seeps in Taylor Valley Antarctica: an example of a subsurface melt event

Abstract The 2001/02 austral summer was the warmest summer on record in Taylor Valley, Antarctica, (∼78° S) since continuous records of temperature began in 1985. The highest stream-flows ever recorded in the Onyx River, Wright Valley, were also recorded that year (the record goes back to the 1969/70 austral summer). In early January 2002, a groundwater seep was observed flowing in the southwest portion of Taylor Valley. This flow has been named ‘Wormherder Creek’ (WHC) and represents an unusual event, probably occurring on a decadal time-scale. The physical characteristics of this feature suggest that it may have flowed at other times in the past. Other groundwater seeps, emanating from the north-facing slope of Taylor Valley, were also observed. Little work has been done previously on these very ephemeral seeps, and the source of water is unknown. These features, resembling recently described features on Mars, represent the melting of subsurface ice. The Martian features have been interpreted as groundwater seeps. In this paper we compare the chemistry of the WHC groundwater seep to that of the surrounding streams that flow every austral summer. The total dissolved solids content of WHC was ∼6 times greater than that of some nearby streams. The Na : Cl and SO4 : Cl ratios of the seep waters are higher than those of the streams, but the Mg : Cl and HCO3 : Cl ratios are lower, indicating different sources of solutes to the seeps compared to the streams. The enrichment of Na and SO4 relative to Cl may suggest significant dissolution of mirabilite within the previously unwetted soil. The proposed occurrence of abundant mirabilite in higher-elevation soils of the dry valley region agrees with geochemical models developed, but not tested, in the late 1970s. The geochemical data demonstrate that these seeps could be important in ‘rinsing’ the soils by dissolving and redistributing the long-term accumulation of salts, and perhaps improving habitat suitability for soil biota. The H4SiO4 concentration is 2–3 times greater in WHC than in the surrounding streams, indicating a large silicate-weathering component in the seep waters.

Solute and isotope geochemistry of subsurface ice melt seeps in Taylor Valley, Antarctica

The McMurdo Dry Valleys of Antarctica are a polar desert region with watersheds dominated by glacial melt. Recent ground exploration reveals unusual surface-fl ow-seep features not directly supplied by glacial melt. Much of this seep water is potentially derived from permafrost, snow patches, refrozen precipitation accumulated in the subsurface, buried glacier ice, or even groundwater from the deep subsurface. Flow features that lack obvious glacier melt sources were identifi ed in archived aerial photographs of Taylor Valley. This valley was surveyed for extant and extinct seeps, and the locations of geomorphic features in fi active seeps were documented. Water samples from seeps were analyzed for major ions and stable isotopes of hydrogen and oxygen. Solute chemistry and isotopic signatures of seeps are distinct from those of nearby streams and glaciers, with the seeps having elevated solute concentrations. All but one seep had water isotopically heavier than water from nearby glaciers and streams, suggesting that seep waters have been substantially modifi ed if they had been derived originally from the same meteoric sources that supply local glaciers and streams. The seeps are important because they compose a previously overlooked component of the desert hydrological cycle. Seep features in the dry valleys are potential terrestrial analogs for the geologically young gullies observed on Mars, which are thought to be evidence of groundwater seepage and surface runoff.

The trace-metal geochemistry of the Lake Tyrrell system brines (Victoria, Australia)

Abstract We have analyzed the waters of the Lake Tyrrell system for the trace metals, Fe, Mn, Pb, Cu and Zn. In a number of samples both dissolved Fe T and Fe 2+ were also determined. Great care was exercized to minimize any contamination of the samples. Not surprisingly the highest metal concentrations occur in the low-pH, high-Eh regional groundwaters, with much lower values observed in the reflux brines and the neutral Wahpool-Timboram waters. It is thought that the source of these metals to the groundwaters is the dissolution of a suite of heavy minerals within the aquifer, the Pliocene Parilla Sand. As the acid groundwaters flow toward the lake some metals are removed near lake edge at depth. The metal concentrations in the spring zone region indicate an extremely dynamic system, where at different times of the year due to changes in the hydrologic regime metals can be either removed or solubilized.

Geochemistry of surface waters of Vojvodina, Yugoslavia

Abstract Major elements data are presented for a number of surface water samples from the Vojvodina region of Yugoslavia. These include samples from the Danube and Tisa Rivers as well as from three lakes in the Pannonian Plain. The data indicate that surface waters evolved to two major water types: Na-CO3-SO4-Cl and Na-Cl. The chemical composition of the surface water from this region has been strongly affected by anthropogenic activities including irrigation and the direct introduction of various chemical species, especially Na and Cl. It appears that the major element chemistry of a number of lakes in this region has changed since the 1950s.

Alabama Gulf Coast groundwaters: 4He and 14C as groundwater-dating tools

Analyses of 4 He and 1 4 C in groundwaters from a Miocene quartz aquifer on the Alabama Gulf Coast show the usefulness of 4 He for dating these Holocene groundwaters. In this aquifer system of low alkalinities and low pHs, radiocarbon ages can be used without model correction. The groundwaters studied ranged from 42.3% to 95.5% modern carbon and yielded uncorrected ages of 375-6790 yr. Radiogenic 4 He ages ranged from >50-7500 yr.

Nitrogen budget of the Mobile–Alabama River System watershed

We have determined the nitrogen mass balance for the Mobile–Alabama River System (MARS) for two years of different hydrologic regimes (i.e. low flow vs. high flow). The maximum riverine export of N from the watershed is only 7%, suggesting relatively high retention and/or losses of N by denitrification within the watershed. Previous investigations of other watersheds within the USA demonstrate export percentages of c. 20–25%. Our calculations indicate that during a high flow year such as 1990, c. 13% of the new N introduced to the watershed annually is lost within the riverine system either through diatom uptake or denitrification. Another 4% is lost to the groundwater while 25–38% is sequestered by the terrestrial biomass (i.e. crop production and forest growth). Thus, as much as 51% of the N input to the landscape in the MARS is unaccounted for. We believe the location of this ‘missing’ N is probably within the soil, or the N has been lost through denitrification within the terrestrial ecosystem. The relatively low N yield from the MARS suggests that the watershed is not as saturated with respect to N as are many other U.S. drainages.

Geochemistry of streams from Byers Peninsula, Livingston Island

Abstract In January and February 2009, a series of water samples were collected from streams on Byers Peninsula. These samples were analysed for major elements and δ18O to determine the role of lithology and landscape position on stream geochemistry, and to understand better the hydrology (i.e. residence time of water) of these systems. Precipitation chemistry is enriched in Na+, as are the streams located close to the coast. Streams originating from inland locations have much higher percentages of Ca2+. In contrast, Mg2+ varied little, though streams that are in greater contact with volcanic-derived soils have slightly higher concentrations. Anion percentages varied greatly between streams with SO42- ranging from 5% to 45% of the anion composition. Dissolved Si concentrations as high as 141 μM were observed. All these data suggest that active chemical weathering is occurring in this region. A time series over 13 days at one stream showed little variation in major element geochemistry. The δ18O of precipitation samples collected over this same period varied by ∼10‰ while the majority of stream samples varied less than ∼1.5‰. These data indicate that the stream waters represent mixtures of precipitation events, melting snow and water from the subsurface that had gained solutes through chemical weathering.