CO2 flux behavior in the maritorium of San Andres Islands on 2019

Comportamiento del flux de CO2 en el maritorio de san Andrés Islas en 2019

Juan G. Popayán Hernández^1*
Orlando Zúñiga Escobar^2*

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^1* Ph.D Candidate in Environmental Sciences, juan.popayan@correounivalle.edu.co ORCID: 0000-0001-7110-3371. Universidad del Valle, Santiago de Cali, Colombia.

^2* Ph.D. Tecnología Agroambiental, orlando.zuniga@correounivalle.edu.co ORCID: 0000-0003-4434-8597. Universidad del Valle, Santiago de Cali, Colombia

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How to cite: J. G. Popayán-Hernández and O. Zúñiga-Escobar, “CO2 flux behavior in the maritorium of San Andres Islands on 2019”, Respuestas, vol. 25, no. 3, 17-28, 2020.

© Peer review is the responsibility of the Universidad Francisco de Paula Santander. This is an article under the license CC BY-NC 4.0.

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Received: June 22, 2020
Approved: October 23, 2020.

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Introduction

The anthropogenic CO2 is emitted in an approximate amount of 35,000 million [1] tons each year, mainly due to the combustion of fossil fuels such as coal, oil and gas. This chemical species has attracted the attention of scientists around the world in recent years because a correlation has been observed between the proportional increase in global temperature [2] and, the concentration of CO2 in the atmosphere [3], [4], which is why it has been attributed as the main precursor to the phenomenon of climate change [5].

In this sense, several investigations show the effects of CO2 on the atmosphere, climate and its consequent effects on some strategic ecosystems [6], [7], since around 46% of CO2 emitted (approximately 16,000 tons/year) [8] remain in the atmosphere for several centuries, there being no consensus around their residence time; What is well known is the proportion of the remaining CO2: 54% [9] is absorbed in the continental and marine ecosystems [8] - [10], the highest proportion being that ending in the oceans, which is estimated between 30 and 40% of the total of the emitted CO2 [11], [12].

Therefore, understanding the behavior of CO2 in the Colombian maritime is essential for the conception of conservation strategies and public policies [13], [14] that allow the safeguarding of marine ecosystems, especially coral reefs [15]. This need is evident when reviewing environmental regulations in Colombia, where there is a gap around the mechanisms for monitoring and mitigating acidification by CO2 in the national maritime.

That is why this article aims to show the behavior of CO2 in one of the main areas of coral reef coverage, San Andres Islands, which is located in the Seaflower Biosphere Reserve, and which houses 3% of the biodiversity of coral species and 33% of fish species, being one of the most diverse ecosystems in Colombia.

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Materials and methods

Study area

The San Andres Islands Archipelago is located in the transition zone between the humid and dry tropics (12- 16 degrees’ latitude N. and 78-82 degrees’ latitude O.). Specifically, the island of San Andrés is 12.8 km long and 3 to 5 km wide, housing a diversity of marine ecosystems, the most relevant being coral reefs, prairie beds, sandy shorelines and, mangroves (16). The study area is shown in Figure I

The CO2 flux is conditioned by the thermodynamic relationships between the solubility of CO2 in seawater, the salinity of the environment, the differential of partial pressures of CO2 in the atmosphere and in the marine environment, and wind speed [17]. Among this group of variables, the action of the wind allows the interaction between the CO2 present in the atmosphere and the surface of some water, due to the action of the waves [18]. In this sense, the behavior of the CO2 flux [19] for the study area is defined from the expression (Equation 1).

Where the CO2 flux (FCO2) is expressed in mmol /m² /day. Where pCO2a is the partial pressure of CO2 in the sea, pCO_2A the partial pressure of CO2 in the atmosphere, S is the solubility of the gas and k is the rate of gas transfer [20].

It is necessary to indicate that the CO2 flux values obtained through the previous one are negative when the ocean captures CO2 and therefore is a sink of this, and they become positive when the study area emits CO2 product of ocean dynamics [21].

Due to the logistical difficulty related to taking the in situ data of the oceanographic variables described in equation 1, each variable was decomposed into a set of physicochemical factors that can be determined from measurements made with remote perception [22].

In this way it has to be that k is a function of the sea surface temperature [23] according to the following expression (Equation 2):

Where U₁₀ is the wind speed at 10 m/s, Sc is the Schmidt number, which is a function of the SST, and the coefficient c and b, which are empirically obtained values.

The transfer speed of a gas, in this case CO2, can be estimated by the relationship between the wind speed and its influence on the transfer constant (k). In this way, it is possible to assume that k is proportional to Sc, which can be obtained from equation 3.

Thus, a third-order polynomial equation is established [24], which is based on the close dependence of Schmidt's number on sea surface temperature (SST) [25] for various gases present in the environment, and their behavior in fresh and marine water [26]. whose empirical coefficients are shown in table I.

On the other hand, the second variable to consider is S, which depends mainly on temperature, pressure and salinity. According to the above, the variation in the solubility of CO2 is relatively low in relation to salinity, since this tends to be constant, while the variation in solubility is more influenced by the sea surface temperature [27], Therefore, the solubility of studies based on an adaptation of Henry's law and the Bunsen solubility coefficients [26], [28] were used, whose values can be seen in Table II:

Finally, the differential between the partial pressures of CO₂ on the sea surface and the atmosphere should be established, for which it is first proposed to calculate pCO₂ (expressed in μatm) in the water from the SST [29] (Equation 4).

Where: A = 6.030; B = -0.06076; C = 0.0007021; D = 0.001655

In this sense, pCO2 (expressed in μatm) will be assumed as constant (350.0 μatm) due to the low variability of the partial pressure of CO2 [30].

Sea surface temperature (SST) data was downloaded from the Moderate-resolution Imaging Spectroradiometer (MODIS-AQUA) sensor [31] available at http://oceancolor.gsfc.nasa.gov/, with a spatial resolution of 4 km and a daily temporary resolution.

On the other hand, wind speed data were obtained from The Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2), a re-analysis of atmospheric data estimated by NASA with the Goddard Earth model Observing System Model, Version 5 (GEOS-5), where georeferenced wind speed information is obtained with a monthly temporal resolution and 1/8 degrees of spatial resolution, available from January 1980 to the present, available at The GES- DISC Interactive Online Visualization and Analysis Infrastructure (Giovanni) (https://giovanni.gsfc.nasa.gov/giovanni/), which processes climatological and oceanographic data [32] obtained from remote sensors administered by NASA.

Finally, with the purpose of calculating CO2 for the San Andrés Islas maritime, 11 points of strategic importance were taken for tourism and fishing activities, and three control points (C), distributed in the coral reef of the Island of San Andres The geographical location of these points is shown in table III.

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Results and Discussion

The behavior of the SST obtained from the MODIS sensor data is shown in Figure II

Figure II shows the dynamics of SST between January and June 2019, showing oscillations between 24 and 31 ° C for this time of year. It can be seen on the maps that the area where San Andrés Islas is located presented an SST of ± 24.5 ° C, with March to April showing average values of 32 and 33 ° C, which is shown in figure III.

In the case of the study area, that is, the San Andrés Islas maritime, it was observed that the surface temperature ranges of the sea did not showconsiderable variation. The oscillation of the surface temperature of the sea oscillated between 24 and 35 ° C, being the months of April and May the ones that showed higher temperatures, which conditions the CO2 flux to the marine environment.

On the other hand, Figure IV shows the wind speed map (U10) obtained from the re-analysis with the MERRA model for the Colombian Caribbean.

In the same way, in figure V, the wind speed map (U10) obtained from the re-analysis with the MERRA model for the sanctuary of San Andres Islands between January and June 2019 is shown.

From ArcGis 10.3, the satellite image information for the SST and U variables was extracted, and with the georeferenced values for the months between January and June 2019, CO2 flux calculations were made using equation 1 The georeferenced data of the CO2 flux is shown in Figure VI..

Figure VI shows that the Colombian Caribbean is not a considerable CO2 sink, at least for the selected period of time. In this sense, the average values of CO2 flux were in the range between 398 and 495ppm in the oceanatmosphere direction, which would be showing that the occurrence of severe acidification phenomena for the Colombian Caribbean seafaring is despised. Despite this, it is necessary to carry out validations of the satellite data, as this would provide greater reliability to CO2 determinations through remote sensing techniques.

For the specific case of the San Andrés Islas maritime, little variability of the CO2 flux was observed, based on the average estimate derived from equation 1, is shown in table IV.

From the values of sea surface temperature and wind speed for the sampling points, the interpolation of the CO₂ flux was obtained, whose ranges are shown in Figure VII.

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Conclusions

From the estimation of the CO2 flux for the San Andrés Islas maritime, it can be said that it does not assume a significant sink trend, since the values for the selected study period were always negative, whose oscillation was between 390 and 405 mmol / m2 / day approximately, discarding considerable acidification processes per CO2 account.

This tendency in the behavior of the CO2 flow positively favors the survival of the coral structures present in the Seaflower reserve, since there is no considerable threat due to the alteration in the process of bioaccumulation of calcium carbonate, the main precursor to coral reefs.

On the other hand, the impact of the CO2 flux on the abundance and distribution of ichthyo fauna is uncertain, mainly of those species of commercial interest for the San Andres Islands root communities. Finally, it is necessary to strengthen the research processes around the behavior of CO2 and its impact on the marine and coastal ecosystems of the Colombian Caribbean maritime.

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Acknowledgments

This article was made possible thanks to the sponsorship granted by COLCIENCIAS through the Call for National Doctorates number 757 of 2016. Likewise, thanks are presented by the authors to COLFUTURO, administrative operator of the sponsorship items of COLCIENCIAS.

To the Research Group on Environmental and Earth Sciences- ILAMA, for the academic support provided to carry out this research.

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