1.    INTRODUCTION

1.1.  The Galápagos Marine Reserve and Marine Ecosystem

The Galápagos archipelago is a scattering of 18 main islands which are peaks of young volcanoes lying about 1000km off the coast of Ecuador.

The Galápagos Marine Reserve was declared in 1998 and includes the interior water of the Galápagos Islands, plus those within 40 nautical miles measured from the baseline of the archipelago. Both the terrestrial and marine areas were declared World Heritage Sites and Biosphere Reserves by UNESCO because they contain, among others, superlative natural phenomena based on biological richness and pristine natural habitats.

The oceanographic interaction between currents and biology in Galápagos is unique. The archipelago is situated at the crossroad of major oceanic currents, combing cold water from the south (Humboldt Current), warm water from the north the goes through the equator (El Niño Current), and a deep, cold and nutrient rich water from the west (Cromwell Current). The mingling of these major oceanic currents has yielded a melting spot of flora and fauna from contrasting environments which partially explain the exceptional marine biodiversity we find today. Mainly the isolation of the archipelago allowed the independent evolution of the species that currents transported up to a point where new species were born. Nearly 20% of marine life is endemic, found nowhere else on Earth. This level of endemism is quite unique for marine species which tend to migrate and intermingle to a much greater extent that their terrestrial counterparts, such as the example of the marine iguana. Galápagos is only place of Earth where the iguana is adapted to a marine ecosystem.

These vital currents have helped the strangest Galápagos creatures like the cold-water penguins to live at this latitude. Indeed, the Galápagos penguins is the northernmost penguin’s species in the world. (Darwin Foundation, 2020). 

1.2.  Influence of Ocean Currents in the flourish of life in Galápagos Islands

Cold and fertile Ocean Currents provide nourishing fields of green algae to the Pacific green turtle, sustaining one of the richest concentrations of green turtle anywhere in the Pacific Ocean. The nutrient rich and cold Ocean Current Cromwell are bathed by the equatorial sun boosting microscopic Phytoplankton productivity that feed the explosion of life. The Galápagos is one few place on Earth where massive concentrations of pelagic species (not closer to coast and not deep in ocean) such as tunas, jacks, barracudas, hammerhead sharks and others, can be seen close to shore because food provision.

The Phytoplankton contains Chlorophyll, a pigment that transforms sunlight into energy the plant can use. This same pigment gives Phytoplankton their greenish color. Chlorophyll absorbs most visible light but reflects some green and near-infrared light. (NEO, 2019).

In Galápagos, corals and fishes from warm tropical Ocean Current El Niño share the ecosystem with sea lions or penguins, more typical from polar areas which migrate due to Humboldt Ocean Current. The marine ecosystem is an underwater wildlife spectacle, no other site in the world can offer the experience of diving with such a diversity of marine life forms that are so familiar with human beings. (Darwin Foundation, 2020).         

2.     OBJECTIVE

Identify the presence of Phytoplankton in Galápagos Marine Reserve which is seasonally influenced by the cold Ocean Current Humboldt and Cromwell, and warm Ocean Current El Niño. 

3.     DATA AND METHODS

The cold Ocean Currents Humboldt (from south) and Cromwell (from west) normally flourish Galápagos after July until the end of the year, with the lowest temperature registered in August with 16°C. On the other hand, the warm Ocean Current El Niño (from north) visits the islands at the beginning of the year having the peak temperature on March with 27°C. 

3.1.  Seasonal Data

This analysis was done with satellite images from Sentinel 3 with sensor OLCI (Ocean and Land Color Instrument). The images were selected from months with peak temperatures registered due to the visit of Ocean Currents. As a result, the Chlorophyll concentration was obtained in the near ocean of Galápagos Islands.

Also, to visualize the influence of the water temperature in the presence of Phytoplankton. The 8 day – AQUA/MODIS dataset of sea surface temperature was used. The 8-day dataset selected contains the days of the Sentinel 3 – OLCI images in March and August. Here, the information of the data is presented.

Sentinel 3 – OLCI:

March 28^th, 2019:              S3A_OL_1_EFR____20190328T155754_20190328T160054_20190329T200754_0179_043_054_2880_LN1_O_NT_002.SEN3

August 14^th, 2019:             S3A_OL_1_EFR____20190814T155411_20190814T155711_20190815T191235_0179_048_111_2880_LN1_O_NT_002.SEN3

Source: Copernicus Open Access Hub. (https://scihub.copernicus.eu/dhus/#/home)

Sea Surface Temperature 8-days AQUA/MODIS

March 22^th – 29^th, 2019:  
MYD28W_2019-03-22_gs_3600x1800 - 0.1 DEGREES.

August 13^th – 20^th, 2019: 
MYD28W_2019-08-13_gs_3600x1800 – 0.1 DEGREES

Source: Nasa Earth Observations (NEO).    
(https://neo.sci.gsfc.nasa.gov/view.php?datasetId=MYD28W&year=2019)

3.2.  Processing

The geo-processing was done in SNAP software which involves atmospheric correction for water, the filter used was C2RCC water processing/OLCI. The parameter used in the C2RCC filter change by seasons. In March the temperature used was 27°C and for August was 16°C, both with salinity 35.5 PSU (IFREMER, 2020). The temperature used represents the average of the Sea Surface Temperature obtained with the stations in different areas of the Galápagos archipelago. (Darwin Foundation, 2020). This filter provides as a product a new layer called conc-chl that represents the concentration of Chlorophyll (Phytoplankton). In order to create a better product a cloud mask was applied that is specified in the workflow (Figure 1).

The Sea Surface Temperature 8 day – AQUA/MODIS dataset didn’t need processing. The dataset was already corrected with cloud mask and represents the information needed. For visualization and map design the software ArcMap was used.

Figure 1. Workflow of Processing

4.     RESULTS

The next seasonal comparisons, shows the presence of Phytoplankton based on the influence of ocean currents. Mainly, it is found that the cold ocean currents flourish the presence of Phytoplankton, as it can be seen in the Cold Season (August) by the presence of Cromwell Ocean Current (Figure 5). On the other hand, in the Warm Season (March) shows lack of presence of Phytoplankton due to El Niño Ocean Current (Figure 3) but with small concentration close to the islands due to Cromwell and Humboldt Ocean Current. 

4.1.  March – The Warm Season

El Niño warm Ocean Current influence the equatorial area of Pacific Ocean, including the surroundings of the Galápagos Islands. As we can see in Figure 2, the warm ocean current has temperatures over 19° C. But, at the same time, there is mixture with the presence of Humboldt Ocean Current that goes directly to the East face of Galápagos Islands which has temperatures mainly of 12°C. The Cromwell Ocean Currents has a slightly influence in this season.

Figure 2. Sea Surface Temperature Warm Season Galápagos 

As a result, in this Warm Season (March) it is observed the lack of presence of Phytoplankton at the north of the islands due to El Niño Ocean Current. But there is concentration of Phytoplankton over 0.25 mg/m³ in the interior of the island and closer to the East islands (green, yellow and red color in Figure 3). This presence is caused because of the influence of Humboldt and Cromwell Ocean Currents. Generally, there is no spatial distribution of concentration of Phytoplankton in Galápagos Marine Reserve in this season.

4.2.  August – The Cold Season

In the Cold Season the influence of El Niño Ocean Current decrease, and the temperatures are not greater than 19°C at the north of the islands. On the other hand, you can see in Figure 4 that Humboldt and Cromwell Ocean Currents are influencing all over the south and west of the islands with temperatures around 12°C.

It is known, that Cromwell Ocean Currents arrive with nutrients and rich of Phytoplankton, and this is visualized in Figure 5. The presence of Phytoplankton shows concentrations over 1 mg/m³ and with maximum of 18.13 mg/m³ in the center of the Galápagos Islands and at the West (red color). Also, the spatial distribution of the Phytoplankton has increased in all surroundings of the islands between 0.25 mg/m³ and 0.5 mg/m³, specially at the East face of the islands (green, yellow and orange color). So, in Cold Season the Cromwell Ocean Current influence significantly the presence of Phytoplankton. The influence of Cromwell Ocean Current is greater than Humboldt Ocean Current considering that both are cold ocean currents.

5.     CONCLUSION

The Cromwell Cold Ocean Current has a significant influence in the presence of Phytoplankton in the West area of the Galápagos Marine Reserve. The influence is greater that Humboldt Ocean Current considering that both area cold ocean currents. The comfortable ecosystem for Phytoplankton has temperature over 12°C and less than 16°C. Over 16°C the Phytoplankton presence decrease. El Niño Warm Ocean Current has no influence in the presence of Phytoplankton in the North areas of the Galápagos Marine Reserve. 

6.     BIBLIOGRAPHY

         DARWIN FOUNDATION (2020). Climatology Database. Retrieved from:            https://www.darwinfoundation.org/en/datazone/climate/puerto-ayora

  IFREMER (2020). Sea Surface Salinity. Retrieved from:   http://www.salinityremotesensing.ifremer.fr/sea-surface-salinity/definition-and-units

              NASA EARTH OBSERVATION. (2020). Sea Surface Temperature (8 day - AQUAMODIS). Retrieved from:     https://neo.sci.gsfc.nasa.gov/view.php?datasetId=MYD28W&year=2019