57. Strong-short-term effects of a volcanic eruption on the carbonate system of a highly stratified fjord in the Northern Chilean Patagonia

Maximiliano J. Vergara (1)*, Rodrigo Torres (2, 3), Emilio Alarcon (2), Cory Beatty (4), Michael DeGrandpre (4), L. Antonio Cuevas (5), José L. Iriarte (3, 6, 7)

1 Programa de Doctorado en Ciencias de la Acuicultura, Universidad Austral de Chile, Puerto Montt, 5501558, Chile
2 CIEP Research Center, Coyhaique, Chile.
3 IDEAL Research Center, Universidad Austral de Chile, Puerto Montt, Chile
4 Department of Chemistry & Biochemistry, University of Montana, Missoula, Montana, USA.
5 Department of Aquatic System, Faculty of Environmental Sciences & Environmental Sciences Center EULA Chile, Universidad de Concepción, Concepción, Chile
6 COPAS-Sur Austral, Universidad de Concepción, Concepción, Chile
7 Instituto de Acuicultura, Universidad Austral de Chile, Puerto Montt, 5501558, Chile

Background
Volcanic explosions can release large quantities of acidifying compounds, and can lead to significant environmental impacts in terrestrial and aquatic systems. From April to May of 2015 the Calbuco Volcano (north Patagonia) started an eruptive process releasing more than 0.21 km3 of ash. Previous studies have shown severe acidification effects from volcanoes and their impact to water chemistry. In this study, we investigated the dynamics of the carbonate system before and after the eruption (April-July) in surface waters of Reloncaví Fjord, a major shellfish farming area.

Methods
High temporal resolution data (every 1h) was collected from a buoy (3.5 m) in the middle section of the fjord (41ºS), for pH, pCO2, temperature, salinity and dissolved oxygen (SAMI-Sunburst; MicroCat-SeaBird). Samples were periodically collected for pH and total alkalinity. Hydro-meteorological data from a weather station (HOBO-U30) and river streamflow were measured at the study area.

Findings
The carbonate system of surface waters of the fjord before eruption showed natural pCO2 increases and pH decreases leading to an unsaturated aragonite state (Ω<1) during winter months (June-July). One month after the eruption (June), the carbonate system showed abrupt acidification at the top surface layer, related to recurrent heavy rain events, where waters reached pH values down to 7.2 (≈ 0.4 pH units lower than one day before). Additionally, aragonite saturation was almost near zero (Ω= 0.05) and abrupt changes in the pCO2 (≈1000 μatm variation) were observed, lasting for more than one week.

Conclusions
This study provides information on how the surface layer of an estuary responds to strong and rapid changes in the acid/base chemistry after a volcanic eruption. The findings suggest that the acidic event after the eruption could be due mainly to the transport of acidic runoff with volcanic materials via tributary rivers to the marine system of the fjord.

71. The Role of Planktonic Foraminifers as Driver of Carbonate Export in the Scotia Sea (Southern Ocean)

Meltem Ok (1,2)*, Gabriele Stowasser (1), Sophie Fielding (1), Geraint Tarling (1) and Clara Manno (1)

1 British Antarctic Survey, Cambridge, Cambridgeshire, CB3 0ET, United Kingdom
2 Middle East Technical University, Institute of Marine Sciences, 33731, Erdemli, Mersin, Turkey

Background
In the Southern Ocean the 20% of the global carbon uptake takes place. The amount of carbon dioxide transferred to the deep ocean is regulated by the carbon (promoting CO2 sink by photosynthesis) and carbonate (producing CO2 source by calcification) pump. Planktonic foraminifers (carbonate producers), contribute up to 50 % of the total carbonate export in the ocean and in the Southern Ocean can represent a dominant component of carbonate flux. Therefore the understanding of foraminifera population dynamic and their response to the forecasted anthropogenic stressors (i.e. Ocean Acidification) is a critical issue.

Methods
Foraminifera samples were collected by deep sediment traps (2000m) deployed at two sites with contrasting ocean productivity regimes (P3, naturally iron-fertilized, and P2, iron-limited). We investigated the seasonal and interannual variability in foraminifera relative abundance. Since global models suggested that iron fertilization could accelerate Ocean Acidification to the deep water, we focus our study on the variability in shell degradation/dissolution between the two sites.

Findings
Despite, foraminifera seasonal trend was similar at both sites with a peak occurring in late summer-early autumn, foraminifera flux was 1 order of magnitude higher at P2 than at P3. The contribution of foraminifera to the carbonate flux was also significantly higher at P2 than P3 (up to 67% and 34% of the total carbonate flux respectively). Preliminary results suggested a higher level of shell degradation at the iron fertilized region compare to the iron-limited ones.

Conclusions
This is the first study showing the important role of foraminifera as driver of the carbonate export in the Scotia Sea. However iron supply does not seems to promote carbonate export by foraminifera precipitation. The understanding of how a decrease in foraminifera population, due to environmental anthropogenic stressors, could impact the balance between carbonate and carbon pump requires further investigation.

74. Decadal Trends of Underway pCO2 Observed from VOS ships in the Tropical Pacific

Catherine E. Cosca (1)*, Richard A. Feely (1), Simone R. Alin (1)

1 National Oceanic and Atmospheric Administration/Pacific Marine Environmental Laboratory, Seattle, WA, 98115, USA

Background
As part of a multi-year effort to quantify the flux of CO2 between the ocean and atmosphere, the Ocean Climate Observation Program of NOAA supports the deployment of underway CO2 systems on NOAA research ships and volunteer observing ships (VOS) in the Atlantic, Pacific and Southern Oceans. For the past decade (2004 – present), PMEL has maintained an underway pCO2 system on 6 different container ships crossing the Pacific Ocean from Long Beach to New Zealand.

Methods
Measurements of pCO2 have been collected from 39 crossings of the Tropical Pacific from Long Beach to New Zealand from 2004 through 2016, capturing data during various ENSO and seasonal conditions. Data are quality controlled locally at PMEL, and globally via the SOCAT community, resulting in a high quality time series of pCO2 and ancillary measurements in the Pacific region.

Findings
A pattern of increased pCO2 distributions across the entire Pacific basin has emerged from the sustained high quality pCO2 measurements PMEL has attained from container ships in the past decade. The decadal difference in pCO2 reaches ~ 36 μatm at the equator, and decreases in the southern latitudes. Of particular note is a dramatic increase of pCO2 in the northern hemisphere due to anomalously high sea surface temperatures known as “The Blob”.

Conclusions
Enhanced carbon distributions in the North Pacific may have strong implications for the oceanic carbon budget for the time frame the anomalously high sea surface temperatures continues to exist, transitioning the region from a CO2 sink to a CO2 source.

73. Constraining net calcification/dissolution in the open ocean using high precision ID measurement of dissolved Ca/Mg ratios in seawater

Ellen V Cliff (1)*, Stephen M Eggins (1), Linda McMorrow (1), Leslie Kinsley (1)

1 Research School of Earth Sciences, The Australian National University, Canberra, 2601, Australia

Background
Laboratory and field studies indicate higher pCO2 waters can effect calcium carbonate shell formation by marine calcifiers such as pteropods, foraminifers and coccolithophores. However, the larger scale effects of changing ocean chemistry on calcium carbonate production and dissolution are less well understood. Changes in dissolved Ca content of seawater has the potential to be used, without ambiguity, to constrain amounts and rates of change of net calcium carbonate production (dissolution) in both the surface and deep oceans.

Methods
We have developed a straightforward, isotope-dilution method for determining dissolved Ca and Mg concentrations in seawater with high precision and accuracy. A single 43Ca and 25Mg enriched spike, designed to minimise weighing errors, is added to seawater samples, which are then diluted and analysed by MC-ICPMS. Measured Ca/Mg molar ratios are used to calculate the excess or deficiency in Ca relative to a source (reference) water composition, assuming Mg is conserved in open ocean samples. This Ca excess/deficiency constrains the net amount of calcification/dissolution that has occurred in the sample relative to source water.

Findings
We have commenced applying the approach to a North-South transect of the Australian sector of the Southern Ocean (SR03 and SAZ lines), in an effort to constrain changes in Ca/Mg relative to upper circumpolar deep water, in surface waters, Antarctic intermediate water and Sub-Antarctic mode waters. We aim to apply and integrate the technique with oceanographic and carbon system observations in an effort to estimate current rates of net calcification and dissolution in Southern Ocean and to search for changes that may have taken place over the past few decades.

Conclusions
We have developed a method for determining the amount and rate of net calcification/dissolution in the ocean that is based on highly precise and accurate analyses of dissolved Ca and Mg in seawater.

72. Surface total alkalinity, salinity and temperature: a study case in the South-western Atlantic Ocean

Leticia Cotrim Da Cunha (1)*, Cintia Albuquerque (1)*, Rodrigo Kerr (2), Iole Orselli (2)

1 Faculdade de Oceanografia, Rio de Janeiro State University (UERJ), Rio de Janeiro – RJ, 20550-900, Brazil
2 Instituto de Oceanografia, Federal University of Rio Grande (FURG), Rio Grande – RS, 96203-900, Brazil

Background
Total alkalinity in open ocean surface waters is mainly controlled by salinity, although processes such as calcification, primary production and respiration may contribute to changes in it. Here we analysed surface total alkalinity samples (AT) from two cruises along the Brazilian shelf break in the South-western Atlantic, from 23°S to 32°S, from 2014 and (planned) 2015. This area of the ocean still lacks CO2-system data, and only recently more oceanographic sampling initiatives for this purpose were taken. Our main objectives are: a) correlate the AT values to surface salinity (SSS) and temperature (SST) in order to assess the role of shelf biogeochemistry; b) check how this area relates to established AT x salinity relationships, and c) provide a simple, robust tool to reconstruct historical data for AT and other CO2-system parameters to this area of the ocean.

Methods
Surface samples (circa 5 metres) were collected and analysed according to Dickson et al. (2007). Total alkalinity analyses were conducted independently in both open and closed cell titration, surface temperature and salinity data were taken from ship CTD measurements. Samples were analysed at both FURG and UERJ laboratories.

Findings
AT data from 2014 was positively related to surface salinity (TA = 50.81SSS + 546.26, R² = 0.90, n = 48) and to SST (TA = 95.34SST + 305.88, R² = 0.47, n= 48), very close to the previous equation proposed by Millero et al (1998) for the Atlantic Ocean.

Conclusions
Preliminary results point to a control on AT by the balance between evaporation and precipitation in the open ocean region, despite Trichodesmium blooms in 2014. There are neither significant alkalinity riverine inputs in this portion of the Brazilian coast nor influence of the Patos Lagoon plume in the southernmost AT samples.

70. Monitoring Carbonate Chemistry of Algal Ridges at One Tree Island Reef using Spectrophotometric System

Vikashni Nand (1)*, Michael Ellwood (1), Steve Eggins (1), Bill Maher (2), Aero Leplastrier (1)

1 Research School of Earth Sciences, Australian National University, Canberra, ACT, 2601, Australia.
2 Institute of Applied Ecology, Faculty of Applied Science, University of Canberra, Canberra, ACT, 2601, Australia.

Carbon emissions and ocean chemistry are factors that affect the corals and reef systems. One component of coral reefs that has received little attention with respect to ocean acidification is the algal ridges that form the margins of many coral atolls and reefs. These ridges form protective features and are typically found on the windward margins of coral islands and atolls. The principal binding and cementing agent of algal ridges is metastable high-Mg calcite (Mg0.14-0.20Ca0.80-0.86CO3); the most soluble carbonate polymorph and consequently the most susceptible to ocean acidification. The aim of this study was to understand the processes that influence production and dissolution of these on algal ridges.

Here we made spectrophotometric measurements of pH and alkalinity of the algal ridges pools at One Tree Island. A number of dome experiments were conducted to quantify carbonate production and dissolution within these algal pools when isolated from the atmosphere and surrounding waters for approximately 3– 4 hours. The algal turf and red coralline algae communities in these algal ridge pools are subject to large diurnal changes in dissolved inorganic carbon (DIC) and alkalinity along with dissolved oxygen due to the accumulation/consumption of products/reactants of photosynthesis, respiration and calcification. During the day the pools show a strong DIC decrease and dissolved O2 increase and a significant decrease in alkalinity (~100 mol/kg, relative to offshore seawater) that reflects the production of high-Mg calcite by the red coralline algae. The ΔAlk-ΔDIC slope is significantly less than a nearby coral-rich back-reef site, which shows a slope near the theoretical 2:1 value for calcification. At night the reef crest pools become highly oxygen depleted (~40% saturated) despite being in contact with the atmosphere, and accumulate large amounts of metabolic CO2 and alkalinity due to the dissolution of a carbonate phase. The trajectory for increasing DIC and alkalinity is close to the equilibrium saturation state for high-Mg calcite dissolution with 15 mol% Mg. Thus the study contributes to a better understanding of. carbonate dynamics on One Tree Island algal ridges.

67. Quantifying the Carbonate Chemistry and pH Fluctuations of Otago Harbour, New Zealand

Katie S Nelson (1)*, Kim Currie (2), Miles D Lamare (1), Judith Murdoch (3)

1 University of Otago Department of Marine Science, Dunedin, Otago, 9016, New Zealand

2 NIWA, Dunedin, Otago, 9016, New Zealand

3University of Otago Department of Chemistry, Dunedin, Otago, 9016, New Zealand

Background

In order to understand the impacts of Ocean Acidification on biological and ecological processes and design meaningful ex situ experimental parameters, it is necessary to quantify variability in the pH and carbonate chemistry of specific environments such as the inter-tidal zone. High resolution and continuous pH and carbonate chemistry datasets are needed to describe the variability in these complex habitats that undergo diurnal and seasonal shifts in both biotic and abiotic factors. To understand the full effect of ocean acidification it is important to answer the question: What is the current pH range and carbonate chemistry patterns experienced in situ in the inter-tidal and sub-tidal zones that is biologically relevant?

Methods

A continuous pH data set was collected over a 42 day period from May – June 2015 with a Satlantic SeaFET and compared to an ongoing light (PAR) and tidal (m) dataset collected at Portobello, Dunedin. Weekly inter-tidal and sub-tidal water samples were collected from March – October 2015 along with temperature, salinity, DO and chlorophyll concentration data. Dissolved inorganic carbon (DIC) and alkalinity (AT) were processed post collection and additional carbonate chemistry parameters were calculated using the program CO2calc.

Findings

Preliminary results are consistent with existing literature, suggesting that large natural variations in surface epipelagic “pH seascapes” are driven by local environmental conditions. The data show that Otago Harbour conditions appear to be driven by two main factors;

1. The primary frequency is driven by large light peaks followed by pH peaks caused by diurnal phytoplankton activity and,

2. The secondary frequency is driven by semi-diurnal patterns associated with tidal fluctuations bringing off-shore water in and out of the harbor.

Conclusions

Benthic invertebrate larvae settling in the inter-tidal or sub-tidal zones are exposed to a large range of pH conditions.

65. Spatial variation of total alkalinity and total dissolved inorganic carbon along the Brazilian continental shelf-break and slope: preliminary results

Mariah Borges (1), Iole Orselli (1)*, Rodrigo Kerr (1)

1 Laboratório de Estudos dos Oceanos e Clima, Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), Av. Itália km 8, Rio Grande, 96203-900, RS, Brasil.

Background
The lack of long-term measurements of carbonate system parameters along Brazilian continental shelf and slope hinders correct characterization of those parameters in this region. Together with questionable and few previous measurements, the accuracy desired to infer about ocean acidification state in Southwestern Atlantic Ocean is still an open question.

Methods
Seawater samples were collected in early spring of 2014 (October) along south and south-eastern continental shelf-break and slope of Brazil to infer about the carbonate system parameters and to correct characterize values of each regional water masses. Another ocean cruise in the area is expected to occur in November 2015. Total alkalinity (AT) and total dissolved inorganic carbon (CT) were determined in a closed cell by potentiometric titration following Dickson (2007).

Findings
It was possible to identify six water masses in the region (temperature°C – T; salinity – S): Plata Plume Water (PPW) with T>10 and S<33.5; Subtropical Shelf Water (STSW), which has two ranges, T>14 and 33.5<S<35.3, and T>18 and 35.3<S<36; Tropical Water (TW), with T>18.5 and S>36; South Atlantic Central Water (SACW) with T>18.5 and S>34.3; Antarctic Intermediate Water (AAIW), with 2 <T<6 and 33.8<S<34.8; and North Atlantic Deep Water (NADW) with 1.5<T<4 and 34.8<S<35. AT ranged between 2200 and 2400 µmol kg-1 and CT between 1950 and 2400 µmol kg-1. AT is highly related with salinity, which decrease towards the seabed. CT is related with temperature and salinity.

Conclusions
This study is a preliminary characterization of the hydrographic and biogeochemistry parameters distribution in the Brazilian continental shelf and slope. A qualitative comparison with available climatology shows high values of AT and CT for these data, reinforcing the need for more sampling efforts. Following steps for this research is to quantify the anthropogenic carbon by distinct methodologies, focusing on estimate acidification state of the region.

55. Decadal scale carbon dioxide increase and acidification in the Weddell Sea, Southern Ocean

Mario Hoppema (1)*, Steven van Heuven (2), Rob Middag (3), Kim Currie (4), Oliver Huhn (5)

1 Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27515, Germany
2 Netherlands Institute for Sea Research, Texel, the Netherlands
3 Dept. of Chemistry, NIWA/University of Otago Research Centre for Oceanography, Dunedin, 9054, New Zealand

4 NIWA / University of Otago Research Centre for Oceanography, Dunedin, 9054, New Zealand
5 Institute of Environmental Physics, University of Bremen, Bremen, 28359, Germany

Methods
Using a suite of cruises spanning several decades, we investigated the time rate of change of Total CO2 (TCO2) and related variables in the surface layer of the Weddell Gyre and adjacent Antarctic Circumpolar Current.

Findings
At the Prime Meridian, a significant TCO2 increase was observed, which is clear evidence for the invasion of anthropogenic CO2. In the Weddell Sea Bottom Water at this location, the spatial distribution of the increase in TCO2 bears a high resemblance to that of CFCs, suggesting that the changes in TCO2 have been propagated from the surface. However, other variables like dissolved oxygen and silicate also show trends through time, pointing to non-steady state conditions which might also affect the derived CO2 increase. Near the tip of the Peninsula, the coldest and most recently ventilated waters, hugging the continental slope, exhibit increasing TCO2 over time despite the presence of sea ice.

Conclusions
This indicates that CO2 uptake and acidification occur although sea ice cover is present for a significant period of the year. The CO2 increases/changes were translated into changes of carbonate ion and pH. Additionally, we show data on the partial pressure of CO2 for the Weddell Sea, in particular on the seasonal cycle and the saturation state. We determined seasonal changes in CO2, i.e., drawdown through phytoplankton, which we compared to seasonal changes in trace metals in this region.

63. Spatial variability of CO2 fluxes in the Gerlache Strait, Antarctica, during austral summer 2015

Eidt, Renata T.1, Kerr, Rodrigo1, Orselli, Iole B. M.1

 

1Laboratório de Estudos dos Oceanos e Clima, Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), Av. Itália km 8, Rio Grande, 96203-

900, RS, Brazil.

 

Background:

Understanding the processes of exchanges between ocean and atmosphere are extremely important when studying the global climate. The Southern Ocean presents an important role in the CO2 fluxes comprehension, due to its large oceanic area, low temperature and considerable seasonality.


Methods:

Measurements of total alkalinity (AT) and total dissolved inorganic carbon (CT) from the Gerlache Strait were made for water samples collected in February 2015 (austral summer). Partial CO2  pressure in seawater (pCO2sw) was determined from AT, CT, temperature and salinity data using CO2calc; atmospheric pCO2 (pCO2atm) was obtained from Palmer Station. From ΔpCO2 and wind speed data (ECMWF-NOAA), CO2 flux was calculated using Wanninkhof (1992) exchange coefficient.

 

Findings:

The fluxes along the Gerlache Strait showed different patterns responding to the influence of waters with distinct origins (i.e. warm waters from the Bellingshausen Sea and salty and cold waters from the Bransfield Strait). pCO2sw  data ranged between 310 and 560 µatm, with the lowest values on the southwest region, a sheltered area influenced by ice melting and continental input. In general, the Gerlache Strait region acted as a weak source of CO2, with a mean flux of 1.2 ± 4.9 mmol m-2 d-1. However, the southwest area showed an average uptake of CO2 (-1.2

± 3.3 mmol m-2 d-1), whereas the northeast area acted mainly as a source of CO2 to the atmosphere (3.6 ± 5.2 mmol m-2 d-1).

 

Conclusions:

As  a  coastal  area  with  high  biological  production  and  strong  seasonality,  the Gerlache Strait represents an important spot for studies involving CO2 fluxes and its temporal and spatial variations.

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