Carbon - Call for Posters

1 - Biospheric carbon residence time between photosynthesis and methanogenesis: evidence from 14CH4 measurements
K. R. Lassey1
1NIWA, Wellington, New Zealand

Methane is a minor though important sub-cycle of the global carbon cycle. All methane emissions to the atmosphere except from geological reservoirs (14C-free ‘fossil methane’) are sourced in the biosphere where the methane is generated either biogenically or as a by-product of biomass burning, from carbon that was previously fixed through photosynthesis. Carbon emitted to the atmosphere as methane subsequently oxidises there to CO2 (with mean life of about 9 years) to become available again for photosynthesis. The mean life of photosynthesised carbon in the biosphere in the methane production pathway is essentially undetermined. The ‘bomb-14C’ pulse of the 1960s and its propagation into the methane cycle provide an opportunity to examine such biospheric carbon dynamics. We examine a global dataset of atmospheric 14CH4 measurements to suggest a mean residence time for biospheric carbon between photosynthesis and methanogenesis of about 6 years (uncertainty ±50%).

2 - Spatial variability in photosynthetic rate, and instantaneous carbon and oxygen isotope discrimination
M.M. Barbour
Landcare Research, Lincoln, New Zealand

Stable carbon and oxygen isotope ratios of CO2 are useful tracers in studies of carbon and water cycling between the terrestrial biosphere and the atmosphere. Interpretation of variation in 13CO2 and C16O18O relies on models describing physical and biochemical processes and their associated fractionations. A layer of complexity not currently quantified or accounted for in canopy models is spatial variation in photosynthetic discrimination within a single leaf.

A new measurement technique, employing tunable diode laser absorption spectrometry coupled to an open gas exchange system, enables online measurement of photosynthetic discrimination at high temporal resolution. Using this system, photosynthetic rates and 13C and 18O discrimination were measured along leaves of a C3 monocot. For the forage cereal Triticale, 13C discrimination increased by 2‰ and 18O by 20‰ from the base to the tip of mature leaves when measured at saturating irradiance. The increase in both 13C and 18O discrimination were associated with variable photosynthetic rates and an increase in the leaf internal conductance of CO2. When numerical averages are compared to flux- and area-weighted averages, the portion of the leaf approximately one third of the way from the base can be shown to provide the most representative area for scaling up.

3 - Simultaneous Measurements of leaf and soil cO2 flux using a tunable diode laser
J. E. Hunt, M. Barbour
Landcare Research, Lincoln, New Zealand

A portable photosynthesis system (Li-6400, Li-Cor) and a through-flow soil chamber were used to continuously measure the gas exchange of leaf and below ground components in pots containing corn, Triticale and a non-planted control. Measurements were made at 4 min intervals over a full diurnal light cycle. A tunable diode laser (TGA100A, Campbell Scientific) was used to measure the concentration and stable isotopic composition (δ13C and δ18O) of the air entering and exiting the chambers. End-member isotope values were determined by short-term incubation of component parts in Tedlar bags, and the evolved gas was measured with the laser.

We determined the isotopic signature of CO2 derived from root respiration, microbial respiration of plant exudates and soil organic matter (SOM) to allow the partitioning of the total flux into component parts. The potting mix was more enriched (corn) and more depleted (Triticale) than the control, indicating that end-member determination of the original SOM was confounded by plant exudates. Using a mixing model to partition the soil respiration, corn roots contributed 25% and Triticale 72% of the below-ground respiration. Non-root respiration was partitioned into pre-existing SOM and more recent plant derived exudates.

4 - PARTITIONING SOURCES OF RESPIRATION IN AN UNDISTURBED FOREST ECOSYSTEM
D. Whitehead¹, P. Millard², A. Midwood², M. Barbour¹,
J. Hunt¹, G. Rogers¹, T. McSeveny¹
¹Landcare Research, Lincoln, New Zeland
²Macaulay Institute, Aberdeen, UK

The key to quantifying whether an ecosystem will become a net sink or source of carbon with changing climate is in the ability to partition the sources of respired soil carbon between autotrophic, Ra, and heterotrophic, Rh, components. Until now, this has only been possible using artificial systems or techniques that require major disturbance. We have developed and tested a new approach to partition the sources of soil respiration in ecosystems, based on the analysis of differences in 13C isotope signatures. This is the first time that the approach has been used in an undisturbed forest system growing in natural conditions. We achieved this using high precision, state-of-the-art tunable laser diode technology for sampling and analysing 13C isotopes in samples of respired air. We measured at 30 random locations in a 40-year-old kānuka forest. The spatial variability of soil surface respiration was attributed to differences in root length density and distances between locations of the samples and the nearest tree. We were able to partition the source of respiration at 24 of the locations and, overall, Rh and Ra each contributed 50% to soil surface respiration.

5 - A new gas extraction device for ice core analysis
K. Riedel¹, P. Franz¹, D. Ferretti^1*, D. Etheridge², A. Gomez¹
¹National Institute of Water and Atmospheric Research, Private Bag 14-901, Greta Point, Wellington, New Zealand, * has left NIWA
² CSIRO Marine and Atmospheric Research, Private Bag No 1, Aspendale Victoria 3195, Australia

Gas bubbles of air trapped in ice can be used to reconstruct Greenhouse Gas (GHG) concentrations from decades to hundreds and thousands of years ago. This information, gained from ice cores drilled in Greenland or Antarctica, helps us to understand the relationship between GHG forcing and climate variability. The changes in the isotopic composition of the trace gases, if measured with sufficient precision and temporal resolution, can be used to understand the causes of the GHG variations.

We present a method for extracting air from ice samples, which is based on a technique developed at CSIRO in Australia. Ice samples of up to 2 kg size are placed in a stainless steel grating flask. Through vigorous shaking the ice grated into small chips releasing the air from the bubbles. With a helium closed cycle cooler the components of the gas sample are cryogenically trapped in a sample vial. The so prepared gas sample can then be analysed in the laboratory at NIWA for the concentration of methane (CH4), carbon dioxide (CO2), carbon monoxide and nitrous oxide and the isotopic signature of 13CH4, and 13CO2. This dry extraction method is preferred since it does not affect CO2 concentrations through formation of carbonic acid in melt water.

6 - Clays for carbon storage in soil and sediment
G. Yuan, B.K.G. Theng
Landcare Research, Palmerston North, New Zealand

Clays have been involved in sustaining ecological functions in soil since time immemorial, such as water and heat storage, element (nutrient) cycling, and biodiversity preservation. The importance of clays to stabilising organic matter in soil and sediment cannot be overstated in the age of ‘carbon civilization’ (Lal, 2007). Little research, however, is being done in New Zealand on the fundamental processes and practical applications of the clay-organic interaction in relation to organic matter storage and stabilisation in soil and sediment (Derenne and Knicker, 2000).

The surface area, porosity, and charge characteristics of clays control and influence their ability to adsorb organic matter and store carbon. These properties of clays can, to some extent, be manipulated (modified) in order to improve performance either in the natural environment or for industrial applications. Here we present a brief review of the reactivity of clays towards organic matter, using allophane-rich soils as an example (Yuan et al. 2000). Such soils are wide-spread in New Zealand because they derive from volcanic ash (tephra). We also describe some future research needs for managing carbon storage in soil.

References

Derrene S, Knicker H. 2000. Chemical structure and preservative processes of organic matter in soils and sediments. Organic Geochemistry. 31:607–608
Lal R. Soil science and the carbon civilization. 2007. Soil Science Society of America Journal. 71:1425–1437.
Yuan G, Theng BKG, Parfitt RL, Percival H. 2000. Interactions of allophone with humic acid and cations. European Journal of Soil Science. 51:35–41.

7 - CARBON SEQUESTRATION BY HYDROTHERMAL CARBONIZATION of Waste biomass
D.N. Dickinson¹, J.P. Kim¹, A.R. Hayman¹, W.W. Dickinson²
¹Department of Chemistry, University of Otago, Dunedin, New Zealand
²Antarctic Research Center, Victoria University of Wellington, Wellington, New Zealand

Hydrothermal carbonization (HTC) is a hydrous-pyrolysis reaction that efficiently dehydrates and condenses raw organic matter into carbonaceous compounds (60-70% C). The reaction proceeds in mildly acidic water at temperatures higher than 180 °C. Carbonization is normally completed in 12 hours, and the carbon-rich materials produced by HTC are long-term stores of carbon akin to lignitic coal.

Our calorific measurements show HTC to be an exothermic process that generates sufficient energy for a sustained reaction. Because of this thermodynamic property, large-scale HTC of waste biomass presents a low-cost approach to atmospheric carbon sequestration. By processing forestry and agricultural wastes, carbon that was destined to be released to the atmosphere through biotic oxidation can be permanently stored in carbonized products.

New Zealand is well poised to develop HTC as a viable method of carbon sequestration. Processing the waste carbon from conventional forestry harvests alone could offset more than 20% of national CO2 emissions. Additionally, carbonized materials produced by HTC demonstrate excellent sorption properties and could be incorporated into agriculture soils to increase moisture and nutrient retention.

8 - MODELLING FOREST-ATMOSPHERE CO2 EXCHANGE – SCALING FROM LEAVES TO REGIONS
A. Walcroft¹, M. Kirschbaum¹, C. Trotter¹, D. Whitehead²
¹Landcare Research, Palmerston North, New Zealand
² Landcare Research, Lincoln, New Zealand

New and existing forests will clearly play a part in policy responses to global climate change. While the scale of interest for policymakers is regional to national over annual to decadal time periods, the exchange of CO2 between forests and the atmosphere begins with processes occurring within the leaf over periods of seconds to minutes. Models are available that span these large spatial and temporal scales, allowing predictions and scenarios to be run at large temporal/spatial scales while still respecting the underlying processes.

A suite of four models is presented that operate across a space/time continuum from instantaneous responses of individual leaves to decadal changes in regional forest ecosystems. Each model is described, outlining key features and assumptions, advantages and disadvantages, and applications.

Issues that are common to models across the range of spatial and temporal scales are outlined. These include model validation, sensitivity and uncertainty analyses, model applications and links between models, and future developments.

9 - LEACHING OF DISSOLVED ORGANIC MATTER FROM PASTORAL SOILS
A. Ghani, M. Dodd, A.C. Mackay¹, K. Mueller, M. Dexter,
AgResearch, Ruakura Research Centre, Private Bag 3123, Hamilton,
¹AgResearch, Grasslands, Private Bag 3123, Palmerston North

Some recent studies from UK and in New Zealand have indicated that pastoral soils are losing between 0.6 to 1 t ton of C ha-1 y-1 over the last 20-25 years (e.g. Bellamy et al., 2005; Schipper et al. 2006). These losses in soil C have serious long-term implications for impacts of climate change on soil carbon. It will also affect a wide range of soil services, including aggregate stability, water holding capacity and nutrient assimilation.

Net loss of C from New Zealand pastoral soils could be due to a number of mechanisms including increased organic matter decomposition rates and loss of C through surface run-off and leaching. New Zealand soils under pasture land use contain significantly high amounts of C and N in dissolved organic forms (Ghani et al. 2007). The current study was carried out to quantify the magnitude of losses of dissolved C and N occurring through leaching in a range of pastoral soils that have been shown by Schipper et al., (2007) to have either lost or gained organic carbon over the last 20 years. Five lysimeters (25 cm diameter and 30 cm depth) were collected from each of six grazed pastoral soils located in Hamilton (2), New Plymouth (3) and Thames (1) areas. Lysimeters were placed in a growth chamber (at 14 hr day light - 10 hr darkness and 20ºC) and leached approximately every 3 weeks with reverse osmosis water. Leachates were analysed for dissolved organic C (DOC), and N (DON), NO3-N, NH4-N. Additional soil samples from top 7.5 cm and 7.5-15 cm depths were collected from the sites closed to where lysimeters were collected. These samples were used to characterised the sites for % soil total C and N, pH, Olsen P, hot-water C.

Analysis of leachates showed approximately 10-fold difference in the amounts of DOC and DON leached between soils. Soils with poor drainage characteristics appeared to leach more DOC and DON. There was no relationship between the % total C or % total N in soils and the amounts of leached DOC and DON, suggesting that mobility of DOC and DON can not be predicted by these components in soils. Only small amounts of N leached as NO3-, NH4+ from these soils. The C:N ratio in soils were consistently 10:1, while in leachate considerably narrower (2-6:1). The narrow ratio would indicate the dissolved organic matter (DOM) was probably of microbial origin. Our results suggest that leaching can explain between 5-30% of the total C and N loss estimated from these soils. DOM was also found in significant quantities from the soils sampled that had gained C and N over the last 20 years. Future work will examine effects of short term perturbations on DOC and DON losses, along with losses of C through respiration and N through gaseous losses? This might help better explain the losses of C and N measured In New Zealand pastures.

References
Ghani A, Dexter M, Carran A, and Theobald P, 2007. Dissolved organic nitrogen and carbon in pastoral soils: the New Zealand experience. European Journal of Soil Science, 58: 832-843.
Schipper LA, baisden WT, Parfitt R, Ross C, Claydon JJ, Arnold GC 2006. Large losses of soil carbon and nitrogen from New Zealand pastures during past 20 years. Fertilizer and Lime Research Centre, Massey University, Palmerston North, Occasional Report No 19: 118-123 pp.
Bellamy PH, Loveland PJ, Bradley RI, Lark RM, Kirk GJD 2005. Carbon losses from all soils across England and Wales. Nature, 437:245-248.

10 - Carbon exchange in adjacent pasture and cultivated paddocks during a summer drought
P. L. Mudge, L. A. Schipper, D.I. Campbell, S. Rutledge.
Department of Earth and Ocean Sciences, University of Waikato, Hamilton, New Zealand.

Recent research has shown that some pastoral soils in New Zealand have lost large amounts of C. To determine if cultivation during pasture renewal could contribute to C loss, we measured CO2 emissions using closed chambers in adjacent cultivated and pasture paddocks. In cultivated paddocks pasture was sprayed, ploughed, power harrowed and rolled. During the 39 day period between rolling and sowing, the cultivated paddocks lost 1505 kg C ha-1 and pasture paddocks 1432 kg C ha-1. The initial stages of this experiment were conducted during a drought and during this time CO2 emissions were significantly higher from cultivated paddocks than pasture paddocks (2.58 and 1.5 µ mol CO2 m-2 s-1 respectively). Following rainfall there was a large increase in CO2 emissions from both cultivated and pasture paddocks (4.47 µ mol CO2 m-2 s-1 and 4.81 µ mol CO2 m-2 s-1 respectively) but there was no significant difference between treatments. Prior to rainfall microbes appeared to be moisture limited with a poor relationship between CO2 flux and temperature. At times following rainfall there was a strong relationship between respiration and temperature, while at other times the relationship was very poor. Fluxes measured using the closed chamber technique will be compared with those measured by a nearby eddy covariance system over pasture on the same soil type.

11 - Dynamics of carbon in new zealand pastoral systems
S. Saggar¹, C. Hedley¹
¹Landcare Research Palmerston North, New Zealand

Quantitative information on carbon (C) inputs and decomposition in soils is essential for understanding soil C dynamics, modeling its turnover, and ensuring farming systems are sustainable in terms of nutrient cycling. We measured pasture C inputs and determined the rates of organic C decomposition in soils varying in P fertility using 14C pulse-labelling technique and 14C-labelled glucose incubations. Changes in microbial biomass and residual 14C concentrations were determined.

The above- and below-ground partitioning of 14C was strongly influenced by the P fertility and slope of each pasture site. The low fertility, and medium & steep slope pastures allocated more 14C below-ground compared with high fertility and low slope pastures. The amounts of C fixed at each fertility class and slope category ranged from 4460 to 12815 kg C ha-1 y-1 and the amounts of C translocated to roots ranged from 2451 to 5510 kg C ha-1 y-1 and to soil from 148 to 930 kg C ha-1 y-1. Carbon decomposition was influenced by nutrient P availability. Our results clearly suggest C transfers and transformations are controlled by slope category and soil fertility, and therefore these factors should be accounted for in estimates of soil C change in pastoral soils.

12 & 13 - Māori and Climate Change: Carbon Sequestration Opportunities on Māori land and Māori Land: A regional learning case study on the Gisborne-East Coast
G. Harmsworth
Landcare Research, Palmerston North, New Zealand

Carbon sequestration, through planting trees or regenerating scrub and forest, is seen as an effective short-term measure to reduce CO2 and meet targets agreed under the Kyoto protocol. Afforestation/reforestation – and limiting deforestation – has the potential to increase carbon storage and achieve sustainable land management goals on less productive land.

A combination of spatial analyses using national biophysical datasets, the Māori land information base, remote sensing methods, land-use capability and land-cover characterisation, and integrated collaborative research was carried out with Māori and Government organisations as part of the Landcare Research’s FRST-funded “greenhouse gas programme”.

Results to date using GIS analyses indicate between 200,000 and 400,000 hectares could be eligible for carbon sequestration on Māori land. We can use this approach to effectively target Māori land blocks with carbon farming potential. Current research on local Māori landholdings examines key issues and process methods for carbon sequestration, engagement, and uptake. This work also helps evaluate existing frameworks and tools for mitigation and adaptation to climate change.

14 - Reforestation of marginal pastoral lands in New Zealand: indigenous forests as Kyoto forest sinks.
C.M. Trotter¹, N.A. Scott, J.A. Townsend, R.H. Wilde, S.M. Lambie, M. Marden,
E.J. Pinkney, A.S. Walcroft, D. Whitehead
¹ Landcare Research, Palmerston North, New Zealand

Offsetting greenhouse gas emissions by accumulating carbon in “Kyoto forests” will be critical in achieving a reduction in New Zealand’s net greenhouse gas emissions to 1990 levels—as agreed under the Kyoto Protocol. Exotic Kyoto forests will account for about 70% of the required reductions. Additional offsets can be created by developing “permanent” indigenous forest sinks—the precursor to which is often regenerating indigenous shrubland. Reversion of marginal pastoral hill-country to shrubland also meets a range of sustainable environmental management objectives: erosion mitigation and soil conservation, improvements in water quality, reduction in river-bed aggradation and consequent flooding risk, and creation of indigenous biodiversity.

Biomass estimation equations based on simple measurements of diameter at breast height have been developed for New Zealand’s most common colonising indigenous shrubland species, mānuka (Leptospermum scoparium) and kānuka (Kunzea ericoides). Estimates suggest this shrubland is itself potentially a relatively high biomass sink (up to 150 Mg C ha-1).

Nationally, about 1.45 Mha of marginal pasture land has the potential to revert to shrubland or indigenous forest if livestock is excluded. This area could potentially accumulate about 3 Tg C yr-1, a significant offset to New Zealand’s annual CO2 emissions, with succession to biodiverse, long-lived indigenous forest.

15 - GREENHOUSE GASES: AN INTEGRATED APPROACH TO REDUCING TERRESTRIAL-BASED NET EMISSIONS
D. Whitehead¹, C. Trotter², S. Saggar², S. Greenhalgh³,
F. Carswell¹, M. Barbour¹, M. Kirschbaum², A. Walcroft², F. Kelliher1, K. Tate², A. Fordyce²
¹Landcare Research, Lincoln, New Zealand
²Landcare Research, Palmerston North, New Zealand
³Landcare Research, Auckland, New Zealand

The programme Reducing greenhouse gas emissions from the terrestrial biosphere funded by the Foundation for Research, Science and Technology until 2015 has a primary focus on process-based studies to measure and model net emissions of the three major greenhouse gases across all land uses. Research also includes forecasting risks and opportunities of future climate change impacts and developing new mitigation possibilities. In recognition of an urgent need, and in collaboration with other providers, there is an emphasis in the programme on a developing framework to integrate impacts and adaptation across biophysical, economic and social dimensions. Progress is underway on the development of a decision support system to quantify the effects of land-use change on long-term net greenhouse-gas emissions, incorporating components of soil carbon and nitrogen dynamics and erosion, at catchment and regional scales.

16 - Carbonzero programme: a certification programme for minimising climAte change impacts
A. Smith,
Landcare Research, Lincoln, New Zeland

The carboNZeroCert TM certification programme is an internationally recognised greenhouse gas (GHG) emissions management and reduction scheme for organisations, products, services and events offering optional mitigation strategies though the provision of credible and verified offsets. Those organisations, products etc. that have completed the four steps; measure (GHG emissions), manage (put in place plans to reduce emissions), mitigate (offset unavoidable emissions) and verify (external audit of the previous three steps) can be carboNZero certified. Joining the scheme provides organisations with access to guidance and tools that assist them to achieve their commitments and meet the requirements of the carboNZero programme. The carboNZero programme applies international best practice to measuring GHG emissions using the GHG protocol for corporate accounting and reporting and ISO 14064-1. The carboNZero programme has grown out of GHG and carbon monitoring research at Landcare Research. Ethical and technical oversight is provided by an Independent Advisory Panel.

17 - Greenhouse gas and trace gas measurements programme in New Zealand
G. Brailsford, S. Nichol, R. Martin, A. Gomez,
NIWA, Wellington, New Zealand

New Zealand is located in the mid latitudes of the South Pacific, where the atmosphere is heavily influenced by the Southern Ocean and is therefore ideal for observations of atmospheric carbon dioxide relatively unaltered by local sources. Since 1970 observations of CO2 have been made at Wellington, and from 1973 at Baring Head (41.41 oS, 174.87 oE). This coastal site is a GAW regional station and is located at the top of an 80m cliff. The site is exposed with either strong northerly or southerly winds dominating the meteorology; air arriving at the site approximately 30 % of the time is from a baseline southern oceanic sector.

Since measurements began the concentration of atmospheric CO2 has risen by over 50 ppm, from 324 ppm to a mean annual concentration of 378 ppm in 2006. During the decade of the 1970’s the average growth rate was 1.2 ppm/yr, and through the 1980’s and 1990’s the rate was 1.5 ppm/yr. Since 2000 the mean annual growth rate has increased to 1.9 ppm/yr. To assist in interpreting contributions to this increase a range of other species are also measured at the site.

18 - A Comparison of The Baring Head And Mauna Loa Atmospheric CO2 Records
A.J. Gomez, G.W. Brailsford, K. Riedel
NIWA, Wellington, New Zealand

The New Zealand atmospheric CO2 record is the longest continuous measurement series in the Southern Hemisphere with its inception first at Makara (1970) followed by Baring Head (1972). The Baring Head background air monitoring station (41.4S, 174.9E), situated on a southern coastal cliff 85 m above sea-level, is a remote site located 12 km southeast of Wellington, New Zealand. Air masses arriving at the site from the south (onshore) are representative of a large part of the Southwest Pacific whereas northerlies are influenced mainly by local terrestrial biotic processes of photosynthesis and respiration. The Southern Hemisphere, due to its large extent of ocean, plays an important role in processes relating to global climate and climate change.

A comparison of the CO2 records from Baring Head with Mauna Loa, the longest continuous record for a Northern Hemisphere site (19.5N, 155.6W), is presented. Both show similar increasing trends and growth rates though the difference in mean mixing ratio at the two stations has widened. In 2007, Baring Head was about 3.0 parts per million (ppm) lower than Mauna Loa compared to only 1.5 ppm in the 1970s. (Note this does not include the altitude effect at Mauna Loa). Changes in seasonality at Mauna Loa are of the order of 5 ppm whereas seasonal changes at Baring Head are closer to 1 ppm. The difference between the two trends and the smaller seasonal cycle at Baring Head reflects the extent of the differences in emissions and biogeochemical processes between the two hemispheres, the Northern Hemisphere governed by the greater land mass and the Southern Hemisphere by the greater extent of oceans influenced by a large polar region. Surprisingly, a comparison of the growth rates and the inter-annual variability (around 1-2 ppm), exhibits strong correlations on a monthly time scale despite the inter-hemispheric atmospheric transport exchange time for CO2 of about 18 months.

19 - Atmospheric 14CO2 at Wellington, New Zealand, From 1958 to 2005: The Rise and the fall
K. Currie¹, G. Brailsford, A. Gomez², S. Nichol², K. Riedel², K. Lassey²,
R. Sparks³, M. Manning4
¹NIWA, Dunedin, New Zealand
²NIWA, Wellington, New Zealand
³GNS, Wellinton, New Zealand
⁴Victoria University of Wellington, New Zealand

Atmospheric 14CO2 concentrations were in a steady state prior to the industrial revolution as the production of 14CO2 by incoming cosmic neutrons in the upper atmosphere was balanced by radioactive decay and uptake by the biosphere and oceans. The burning of fossil fuels has diluted the 14CO2, while atmospheric testing of nuclear bombs in the 1950s and 1960s added large amounts of “bomb” carbon into the system. 14CO2 concentrations in the atmosphere have been measured near Wellington, New Zealand since 1954, comprising the longest record in the world. 14CO2 increased from a background level of -10 0/00 in 1955 to a peak of 690 0/00 in 1965 due to the input of bomb derived 14C. The concentration then decreased exponentially with an e-folding time of 17.5 years to the present day level of 76 0/00. The decrease is due to the cessation of the majority of atmospheric nuclear bomb tests, fossil fuel dilution, oceanic and terrestrial uptake, and atmospheric mixing processes.

20 - The southwest pacific ocean – a sink for atmospheric carbon dioxide
K. Currie¹, M. Reid², B.Macaskill³.
¹NIWA, Dunedin, New Zealand
²University of Otago, Dunedin, New Zealand
³NIWA, Hamilton, New Zealand

The Southern Ocean is recognised as a sink for carbon dioxide, low pCO2 in the surface waters and high transfer velocity characterised by high wind speeds combine to give large CO2 fluxes into the seawater. The uptake is variable on both spatial and temporal scales, and the mechanisms affecting the variability are still not well known

pCO2 in the surface waters of the South West Pacific Ocean has been measured on five voyages with spatial coverage including the Tasman Sea, subantarctic surface water, subtropical water and the subtropical and subantarctic frontal systems.

We present the combined data set, and make an estimate of the air-sea carbon flux for the New Zealand region. In general, water south of the subantarctic front (T < 7 oC) has the highest pCO2 measured: 360 – 380 atm; subantarctic water (8 < T < 12 oC) has pCO2 between 330 and 360 atm, and the subtropical water (T > 14 oC) varies from 350 ± 5 atm in the Tasman Sea, to 340 ± 10 atm north of Chatham Rise in the Pacific Ocean.

21 - CO2 in subantarcitc surface water: a time series study
K. Currie¹, M. Reid²
¹ NIWA, Dunedin, New Zealand
²Univesity of Otago, Dunedin, New Zealand

A time series transect has been established in subantarctic surface water off the south east coast of New Zealand. The 60 km long transect extends from the coast (45-46.20 oS 170-43.20 oE) to a station at 45-50.00 oS 171-30.00 oE. and sea surface temperature, salinity and pCO2 have been measured bi-monthly since 1998 . SST, pCO2 and pH of the subantarctic surface water show seasonal cycles that can be fitted with simple harmonic curves. Temperature has a mean value of 10.4 oC, with an amplitude of 2.1 oC, the maximum occurring in late summer. pCO2 has a mean value of 360 atm, an amplitude of 10 atm, the maximum occurring in early spring. The phase of the pCO2 and temperature curves are offset by 158 days, indicating that change in sea water temperature is not the major factor affecting pCO2 in this area. The relative effects of temperature, biological utilisation and air-sea gas exchange on the seasonal change in pCO2 are determined using a simple model. The model results reproduce the timing of the observed pCO2, however the amplitude of the changes is not well reproduced.

22 - Results FROM tHE Total carbon column observing network tccon
V. Sherlock^₁, B. Connor², P.Wennberg³,R. Washenfelder³,G. Keppel Aleks ³, D. Wunch³,G. Toon⁴, J-F. Blavier⁴, D. Griffith⁵, N. Deutscher⁵, J. Notholt⁶, R. Macatangay⁶,T. Warneke⁶
¹NIWA, Wellington, New Zealand
²NIWA, Lauder, New Zealand
³California Institute of Technology, Pasedena, USA
⁴Jet Propulsion Labroratory, Pasedena, USA
⁵University of Wollongong, Wollongong, Australia
⁶University of Bremen, Bremen, Germany

Improved understanding of the processes which control the atmospheric abundance and distribution of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) is needed to make accurate predictions of future climate.
Inverse model estimates of regional-scale surface trace gas exchange using
measurements from the in-situ network are sensitive to errors in modeled transport [Denning et al., 1996; Gurney et al., 2002]. Modeling studies indicate column-integrated trace gas measurements can provide complementary information provided they are sufficiently precise and accurate [Rayner and O'Brien, 2001].

The Total Carbon Column Observing Network (TCCON) is a global network of ground-based Fourier Transform spectrometers (FTS). These instruments acquire near-infrared solar absorption spectra at high spectral resolution which are then analysed to derive precise estimates of the column densities of CO2, N2O, CH4, CO, HF and O2. We give a brief overview of the TCCON initiative and present time series of the column average CO2 volume mixing ratio derived from spectra acquired at four TCCON sites since mid-2004. Preliminary comparisons of FTS and in-situ measurements of CO2, N2O and CH4 made in New Zealand are also discussed.

23 - Characterisation of Soil-Derived Organic matter in New Zealand’s Sedimentary Cascade
K.M. Rogers,¹ W.T. Baisden,¹ B. Gomez, ², M. Page¹, R. Boys³, R. Parfitt,⁴
N. Preston,³ and J.C.Neff ⁵..
¹National Isotope Centre, GNS Science, Lower Hutt, New Zealand.
²School of Geology, Indiana State University, USA
³Research School of Earth Sciences, Victoria University of Wellington, New Zealand
⁴Landcare Research, Palmerston North, New Zealand
⁵Geological Sciences and Environmental Studies, Colorado University, USA

Identifying soil-derived organic matter (OM) in sedimentary systems is the first step in quantifying carbon (C) stabilization and burial. Following on work suggesting that erosion and burial lead to significant global C sequestration and that New Zealand’s rivers transport large quantities of eroded C, we investigate tools for identifying the sources, nature and fate of soil-derived OM in sediments. We identify OM concentrations, C and N stable isotopes, radiocarbon ages and OM chemistry as useful tools for identifying sources. Rock-derived riverine sediments typically have less than 1%C, while surface soils exceed 4%C. Rock and soil-derived sources can be partitioned based on radiocarbon age, while different rock inputs to sediments are separated by up to 2‰ in 13C. Within soils and sediments, d15N shows multiple sources of variation, including agricultural intensification of nitrogen cycling, soil depth, and rock type. The chemistry of OM identified by pyrolysis-GC-MS provides an additional constraint, showing large variation in major compound classes between and within flood events