Part2-II. Carbon Flux in Epigenic Karst Processes

II. Carbon Flux in Epigenic Karst Processes

CARBONATE DEPOSITION/DISSOLUTION CYCLES
AND CARBON DIOXIDE FLUX IN THE PLEISTOCENE

John E.Mylroie
Department of Geology and geography,
Mississippi State University, Mississippi State, MS 39762

The ice core record from Greenland and Antarctica indicates that Late Quaternary atmospheric CO₂levels were elevated during glacio-eustatic sea-level highstands,and were at a minimum during sea-level lowstands. Some investigators have hypothesized that this CO₂flux is driven by carbonate bank submergence cycles, which leads to the deposition of CaCO₃ and the release of CO₂ based on the formula:

Ca⁺⁺ + 2HCO₃^- = CaCO₃+ H₂O + CO₂

It was further hypothesized that the CO₂thus released would help drive global warming and terminate glaciations. This argument is patently false, as global warming and glacial melting are a prerequisite for bank flooding. The opposite consideration may have value, however , in that as soon as sea level lowers enough to expose carbonate banks, release of CO₂by CaCO₃ deposition ceases and sequestering of CO₂as HCO₃^- begins. This change in CO₂may lower atmospheric levels and assist continued global cooling.

The global area of carbonate bank subject to glacio-eustatic submergence/emergence cycles is estimated to be 6´ 10⁵km². During submergence , these banks release bicarbonate CO₂at the rate of 200 g /m² /yr. of carbon. Average submergence cycles last 10 ⁴ years, releasing 1.2 ´ 10¹⁸grams of carbon as CO₂. During emergence, CO₂is sequestered as bicarbonate by dissolution of CaCO₃ , driving the equation above to the left. Studies of carbonate dissolution rates through rock volumes indicate that 75 m³ /m² / yr. of CaCO₃ is dissolved. Given Quaternary limestone densities of 2.0 g / cm³, this is equivalent to 18 g/ m ² /yr. of carbon sequestered. Average bank emergent cycle last 10⁵ years, sequestering 1.1 ´ 10¹⁸g of carbon.

The amount of carbon as CO₂released during submergence cycles approximately equals that sequestered during emergence cycles, indicating no net loss or gain of CO₂ as regards carbonate banks during the Quaternary. During submergence, deposition is mostly as a layer on the bank surface, whereas during emergence , dissolution takes place both on the surface and throughout the volume of the exposed bank. This difference in the location of carbon flux allows banks to keep up with subsidence.

The geochemical cycle of CO₂in a carbonate rock area, Akiyoshi-dai Plateau (Yamaguchi Prefecture, Western Japan)

Kazuhisa Yoshimura
Department of Chemistry, Faculty of Science, Kyushu University, Japan
Youji Inokura
Research division of University Forests, Facluty of Agriculture, Kyushu University, Japan

The geochemical cycle of CO₂ in a carbonate rock area, Akiyoshi-dai Plateau (Yamaguchi Prefecture, Western Japan), one of the biggest karst plateaus in Japan, has been studied, from the daily data of the calcium concentration and the runoff data obtained by continuous measurements of the runoff issuing from Akiyoshi-do Cave, which has the biggest drainage basin in Akiyoshi-dai Plateau,18.5 km² , the following results were obtained: the calcium concentration of the baseflow in the area showed seasonal fluctuations, following change in CO₂ concentration in the soil. Soil CO₂ , measured in the meadows which cover most of the area, varied from a minimum of 0.08 % at a soil temperature of 3.8° C, to a maximum of 1.2% at 20.8° C. The calcium concentration in the groundwater is controlled by the water-limestone dissolution equilibrium, under open system conditions depending on the meadow’s soil CO₂ concentration . At the groundwater runoff peak, the calcium concentration increases due to the flushing out of long-residence water from the deeper phreatic zone. During 1983 - 1986, a yearly average of 2,100 tons of limestone was dissolved in 2.1 ´ 10E + 7 m³ of groundwater issuing from Akiyoshi-do cave, whose catchment basin includes 16.5 km² of a limestone area: the mean solutional denudation rate is 51 mm / ka.

_{The total amount of CO₂ utilized by chemical weathering
in carbonate rock areas all over the world, corresponding to the same amounts of
chemically weathered in carbonate rocks in mol, were estimated by using a limestone
denudation rate of 50 mm / ka and found to be 8´ 10E + 11kg/y.
The role of chemical weathering in carbonate rocks cannot be ignored in the geochemical
cycle of CO₂. To estimated the more precise total global carbon flux volume
from limestone areas, further studies in international collaboration should be necessary.

SOIL CARBON DIOXIDE CONCENTRATIONS AND CLIMATE IN A HUMID SUBTROPICAL ENVIRONMENT

Rudi H. Kiefer

University of North carolina at Wilmington

Soil carbon dioxide content,temperature, and moisture were measured
biweekly for one year at Pigeon Mountain, GA. Levels of soil CO₂ ranged from
0.04% to 2.4 % and were highest during the growing season, lowest during the winter. Soil
temperature correlated positively with soil CO₂ ,accounting for 90% of CO₂
variation. Soil moisture variations decreased CO₂ concentration at times of
high soil water content when CO₂ was flushed downward, and also at times of low
soil moisture content when CO₂ production was inhibited. A predictive model of
logistic from using 14-day means of daily actual evapotranspiration fit the data well ( R²=
0.83). The model also tested well against soil CO₂ data acquired in the coastal
plain at rocky point, NC. If actual evapotranspiration rates are known, the model permits
estimation of soil CO₂ without preliminary field work, and can be used for
studies of karst denudation, which require soil CO₂ data for seasonal and
regional comparison of solution rates. Key words: soil CO₂ , actual
evpotranspiration, karst, denudation, seasonality.

CONCENTRATIONS AND CONTROLS OF SOIL CARBON DIOXIDE IN SANDY SOIL IN THE NORTH CAROLINA
COASTAL PLAIN

R.H.Kiefer & R.G.Amey

Forty-four measurements of soil CO₂ were conducted from
October 1988 to October 1989 at 1-2 week intervals in the Leon Sand of the North Carolina
Coastal Plain at Wilmington. Concentrations were highest in the summer ( mean soil CO₂
= 0.74% on 31 Aug.) and lowest in the winter (mean soil CO₂ =0.20% 0n 26 Jan ).
CO₂ concentrations increased with depth in the root zone from d=30 cm to d=90
cm, but consistently low values were encountered at d=120 cm beneath a hardpan layer.
Statistical correslations were highest between mean soil log pCO₂ and soil
temperature (r=0.77). Daily minimum air temperature was also a limiting factor (r=0.67).
Correlations were weaker for log pCO₂ and potential evpotranspiration (r=0.63)
as well as actual evapotranspiration (r=0.52). Soil moisture content, deficit, and surplus
were not correlated with soil log pCO₂ . Precipitation was negatively
correlated with mean log pCO₂ (r= -0.83 winter, r= -0.54 summer ) , indicating
that rainfall had a "flushing" effect on soil CO₂ which was more
pronounced during the cold season. However, increases in soil CO2 content during times of
high soil moisture were also observed at times.

Hourly measurements were conducted for a 24 hour period on 7 to 8
July,1989 at a Leon sand site with no hardpan. Concentrations measured at 15, 30, 60, 90,
and 120 cm increased with depth. Highest mean soil CO₂ level (0.50%) was
measured at 0600 EST, lowest at 1900 EST (0.41%). Correlations with soil temperature were
negative, especially at shallow depths (r= -0.64 at d=15cm), suggesting that drying of the
soil was a limiting factor . Wind speed was not correlated with soil CO₂.

In sandy substrates, Soil CO₂ levels are largely controlled
by temperature fluctuations and changes in soil moisture content. However, local factors
such as proximity of individual roots, and vertical differences in diffusivity,also play
an important role. In the present study, the greatest weathering potential was found in
the months of July and September, when high soil CO₂ concentrations coincided
with high totals of soil surplus water.

CARBON FLUX MONITORING AT HAWKINS

RIVER SITE, USA

C.G. Groves

Western Kentuky University

For eighteen months I have been involved with Mr. Joe Meiman in a
monitoring project at Mammoth Cave National Park , in Kentucky ( USA), where we have
instrumentation to continuously monitor carbonate water chemistry and flow conditions in
two large underground rivers. At the points of measurement, which we call the Hawkins
River Site, the streams drain a total of about 160 square kilometers of very well
developed karst, and the drainage areas are well defined. This monitoring program is
ongoing. We have used the site to learn about how limestone dissolution rates vary
seasonally and during storms. Although there have been a number of talks about the project
( including in Guilin), the first papers are still in the preparation stage.

With the information we are collecting at Mammoth Cave, I think that
there is a possibility to learn a great deal about the CO₂ flux through the
karst aquifer here, and potentially this could lead to a better understanding of the
interactions between these processes and atmospheric carbon. I thus think that this
project could be very well related to Project 379. I also have a proposal currently under
evaluation that will hopefully supply funding for a gaseous CO₂ analyser so
that these gases can be studied in the soils and the vadose zone of our field site, as
well as other sites.

I would like to propose that the Hawkins River site be considered for
integration into Project 379, and that Mr. Meiman and I could contribute to the project
goals.

CARBON FLUX AT KARST OF ROBERTSON AND JOHN EVANS GLACIERS}

Martin Sharp
University of Alberta, Canada

I am interested in participating in IGCP-379. I am currently involved in work at two sites - Robertson Glacier, Alberta, and John Evans Glacier, Ellesmere Island - on the weathering of carbonate rocks in subglacial and ice marginal environments. One of the main aims of the work is to determine rates of CO₂ consumption in weathering reactions in glacierised carbonate terrains. This seems central to the aims of the IGCP project. Please keep me informed of the work of the project. As yet we have no publications on our work at Robertson/ John Evans Glaciers. these studies have only been running since 1994, and we are still collecting and analysing samples.

I include some details of the sites and the work in progress. Please feel free to use the information in the newsletter if you wish.

Robertson Glacier, Kananskis Country, Alberta: Bedrock consists of Upper Devonian limestones and dolostones . Temperate Glacier.

John Evans Glacier, Ellesmere Island: Bedrock consists of middle Cambrian to lower Devonian limestones, dolostones and evaporites. Polar Glacier.

Objectives of the work are

1. to identify major weathering processes and pathways in the glacial environment, with a particular emphasis on documenting differences between glacier hydrological sub-environments. This work involves analysis of major cation, anion, dissolved Si chemistry of waters, together with their PH.

2. to identify those components of bedrock (often trace components) which are most actively weathering using Sr and S isotopic measurements on meltwater solute;

3. to identify the major carbon sources using C isotope ratios on dissolved HCO₃^-; there is particular interest in the role of microbially mediated oxidation of organic carbon as a means of generating CO₂ and protons for weathering in the subglacial environment;

4. to determine rates of chemical weathering within the glacierised catchments and evaluate rates of consumption of atmospheric CO₂;

5. to determine the extent to which calcite precipitation in sub/proglacial environments results in release of CO₂ to the atmosphere;

6. to evaluate the impact of sulfide oxidation and evaporite dissolution as influences on the net consumption/release of CO₂ in carbonate weathering/precipitation process in glacial environments.

The work is being carried out by M sharp, R Creaser and M Skidmore in the Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton.

RATES OF CHEMICAL DENUDATION AND CO₂ DRAWDOWN IN A GLACIER - COVERED ALPINE CATCHMENT

Martin Sharp, Martyn Tranter, Giles H. Brown, Mark Skidmore

Solute fluxes from a glacier-covered alpine catchment are partitioned into components derived from sea-salt, acid aerosol, dissolution of atmospheric CO₂, and crustal weathering. The bulk of solute is crustally derived. Coupled sulfide oxidation and carbonate dissolution ( SO-CD) and carbonation of carbonate minerals generate approximately equal amounts of solute. Chemical denudation constitutes<1.5% of solid denudation but is significantly higher than the continental average. CO₂ drawdown by weathering reactions varies directly with discharge and suspended-sediment load and inversely with meltwater p(CO₂). If it is generally true that flushing rates control CO₂ drawdown in glacier-covered catchments, then glacially driven chemical weathering could be a significant factor in carbon cycling and climate change on glacial-interglacial time scales(Geology, 1995, vol.23, p61-64 ).

SPANISH GROUP FOR IGCP 379

_{J.C. Canaveras

Museum of Natural Sciences, Madrid

We are interested to establish the IGCP-379 Spanish Working Group. In a
first informal meeting we have established the next objectives and research emphases for
the Spanish WG:

-in-situ monitoring of environmental parameters of on-going karst
processes in different Spanish caves and karst systems, in order to compare with others
countries and geologic/climatic environments.

-paleoclimatic reconstructions based on karst records.

-cooperation with the Spanish WG on INQUA Terrestrial Carbon.

At the beginning the Spanish WG would be formed by, at least,10-15
members.

We already contacted with the president of the IGCP Spanish
Committee(Prof. M. Lamolda). He suggested that firstly a Provisional Working Group must be
formed, which will be officially approved in the next IGCP Spanish Committee Annual
Meeting (June,1996).
_{In this work we will send you two abstracts to the 30th IGC about
our recent researches about microclimate parameters in Spanish caves.

CAVE AIR CARBON DIOXIDE CONCENTRATION AND MICROCLIMATE PARAMETERS IN CANDAMO CAVE

(NORTH SPAIN )}

M.Hoyos, V.Soler, S.Sanchez-Moral, J.C.Canaveras, E.Sanz-Rubio

Museo Nacional Ciencias Naturales, C.S.I.C. Madrid, Spain

Environmental studies are carried out in Candamo Cave
(Asturias,northern Spain) from the results of different microclimate and chemical
parameters. Candamo cave belongs to a relict polygenic karst system developed from early
Pleistocene on Paleozoic limestones. This cave , which contains Paleolithic(18,000-13,000
B.C.) rock art, was closed in 1979 because of the great deterioration caused by mass
tourism. The local climatic conditions are temperate and sub-humid. The environmental
studies were developed from 1989 to 1994, and data were collected by means of an automatic
monitoring system. The measurements were focused on: (1) characterization of the natural
micro-environmental conditions within the cave ( temperature, relative humidity, carbon
dioxide, radon, hydrochemistry ); (2) evaluation of the human impact on these
environmental parameters during experimental periods of visits, in order to calculate a
visitor carrying number for the cave.

The air temperature in the internal part of the cave ranges from 14.25^{^o}C
(spring) to 14.75^{^o}C (autumn ). During the
experimental visit period a maximum increase of 0.15^{^o}C
was measured. The relative humidity always ranges from 94 to 100%, and visitors
seem to have no influence. The recovery time of the cave air was estimated in
approximately 14 hours by means of Rn data. The cave air CO₂ concentration is
highly influenced by external climatic conditions: CO₂ contents range from 1000
to 3000 ppm during autumn, winter and spring, which coincides with high variable
atmospheric pressure values, high rainfall rates and higher air temperatures in the
internal part of the cave than in the external part. During summer the CO₂
concentration and its oscillations range are lower (400-500ppm ) , which coincides with
lower fluctuations of the atmospheric pressure and higher air temperature in the external
part of the cave than in the internal part. During the experimental visit period CO₂
content increased 100-110ppm.

The measured Pco₂ in karstic waters are higher than measured
Pco₂ in air. This indicates that meteoric waters transport the CO₂
to the cave after passing through a well-developed vegetation cover located in the upper
external part of the cave. This is in agreement with the sub-humid and temperate local
climatic conditions and with the CO₂ high concentrations (1600-8375ppm )
measured in organic rich soils of the external part of the cave.

Air temperature and CO₂ concentration have result to be the
most susceptible parameters to be modified by visitors. The variations recorded in these
parameters can also have an important influence in chemical equilibrium conditions of
karstic waters. Regarding to the obtained data we established an optimum visitor carrying
number of 30 people/day, which has been accepted for the re-opening of the cave in 1995.

MICROCLIMATE PARAMETERS IN A MASS-TOURISM CAVE: NERJA CAVE (SOUTHERN SPAIN)

M.Hoyos, V.Soler, J.C.Canaveras, S.Sanchez-Moral, E.Sanz-Rubio

Museo Nacional Ciencias Naturales, C.S.I.C. Madrid, Spain

The carbon dioxide concentration in karst atmospheres is derived from
two main sources: exterior atmospheric CO₂ and biogenic (soil-derived) CO₂.
The distribution and evolution of cave air CO₂ concentration is related to
geomorphologic features (such as cave or conduit dimensions ) and atmospheric parameters
(such as temperature, relative humidity and atmospheric pressure ). All of these features
and parameters can be ‘disturbed’ by human activities.

Nerja Cave is located in the southern part of Spain belonging to a
complex polygenic (upper Pliocene to middle Pleistocene ) karst system developed on
Triassic marbles. The climate in this region is warm and dry. Vegetation in the catchment
area of the cave is scarce or absent, and karstic water circulation is reduced to
infiltration in the seasonal rainy periods. The number of visitors to this show cave is
approximately 500,000 per year, with a maximum of attendance during summer (more than
20,000 visitors per week in August). Data of environmental parameters (temperature,
relative humidity, CO₂ concentration,...) from both visitable and non-visitable
zones were collected automatically by means of a monitoring system installed since 1985.

The cave air temperature increase from the entrance to the interior of
the cave. This increase ranges from 6 to 7°C in winter (
external part: 13.1-15.7^{^o}C; internal part: 21.1-22.9^{^o}C)
and from 2.5 to 5^{^o}C in summer (external part:
16.2-18.7^{^o}C; internal part: 18.9-21.9^{^o}C
) respectively. Seasonal oscillation range from 2.5 to 3^{^o}C,
whereas daily oscillations are lesser than 0.5^{^o}C. The
visitors provoke a rapid increase of 0.3-0.6^{^o}C on
cave air temperature being the recovery times quite variable and influenced by the season
and/or the number of visitors. the cave air relative humidity ranges from 60 to 100% and
is firstly influenced by the water circulation and secondly by the temperature.

The cave air carbon dioxide concentration in winter is 450-550ppm in
the external part, 520-600 ppm in the internal part and 400-450 ppm in the non-visitable
part. In summer the carbon dioxide concentration increases and it is more variable with
values of 700-2000 ppm, 750-1500 ppm and 520-1000 ppm in the external,internal and
non-visitable parts respectively. Daily oscillations are higher in the external part where
air circulation is more effective. The carbon dioxide concentration is clearly influenced
by the visitors and by exterior atmospheric pressure. These relatively low CO₂
values also are diagnostic of a non-organic source, which is consistent with semi-arid
regions with scarce or absent well-developed vegetation cover.

SOIL AS REGULATING SYSTEM IN KARST

K.E.Pustovoytov

Russian Academy of Sciences

I have received the information on " The international Geological
Correlation Program IGCP 379 ‘Karst Processes and the Carbon Cycle’
(1995-1999)". The project is of great interest for me and I would be glad to
participate in it.

My Ph.D. dissertation (Moscow State University, Soil Science Dept.,
1994) was concentrated on the indications of leaching-accumulation processes in Siberian
soils and their paleoenvironmental significance. The soil carbonate accumulations turned
out to be the most informative in this connection. Since about 3 years I have been working
at the radiocarbon laboratory ( Institute of Geography, Russian Academy of Sciences ). At
the present time I have got a number of radiocarbon datings of soil carbonates from
Siberian , Crimea Peninsula (Ukraine) and Troi (Turkey). In the latter case there is a
good possibility to prove the validity of radiocarbon dating by correlating radiocarbon
and archaeological ages. Combining the radiocarbon dating with another soil methods (
micromophology, mineralogy a.o.) I do hope to be able to evaluates and identify the
chronological stages of carbonate-illuviation in its relationship with another processes
in soils.

Within the framework of the project "Karst Processes and the
Carbon Cycle"the following points would be especially interesting for me:

Goal and Objectives-1 and 4,

Research Emphases-Focus 3.

The more detailed topics, coinciding with my experience in the best
way, could be:

-soil as regulating system in the karst phenomena;

-rates of dissolution-accumulation processes by the radiocarbon dating;

-speleothems and soil carbonate accumulations as sources of
paleoenvironmental information.

The main papers reflecting the results of my previous work:

1). Pustovoytov K.E. The Holocene history of relic tundra-steppes: soil
record. 1995. Terra Nostra. Schriften der Alfred-Wegener-Stiftung.2.International Union
for Quaternary research, C I V
International Congress. August 3-10, Berlin. p.224

2). Pustovoytov K.E., Targulian V.O. Illuviation coatings on coarse
fragments as a source of pedogenetic information. 1996. Eurasian Soil Science. v. 29.
No.3. pp.1-12.}