The global ocean is made up of five major ocean basins: the Pacific, Atlantic, Indian, Southern and Arctic Ocean. The Pacific Ocean is the largest of these basins as well as the deepest. Its expanse runs 155 million square miles and contains “more than half of the free water on earth.” Not only is it the largest and deepest ocean basin, but it is also the oldest, comprised of rocks that have been dated to be 200 million years old. You may have heard the term “Ring of Fire” associated with the Pacific Ocean. This name stems from the fact that the Pacific Ocean is prone to earthquakes and formation of submarine volcanoes along its extensive ridge and trench systems.
Ring of Fire
http://oceanexplorer.noaa.gov/explorations/05fire/background/volcanism/media/tectonics_world_map.html
The Pacific Ocean gained its name in the 16th century from the Portuguese navigator Ferdinand Magellan. Magellan and his crew set sail from Spain in 1519 in search of the Spice Islands located to the northeast of Indonesia. The Spice Islands were the largest producers in the world of spices such as nutmeg, cloves, and pepper. They navigated through the Atlantic Ocean and around the tip of South America after which they came across an unfamiliar ocean. He called this ocean ‘pacific’ which means peaceful. Unbeknownst to them, they still had a long journey to the Spice Islands. You can learn more about the voyage of Magellan and his crew here.
Magellan’s Voyage
http://news.bbc.co.uk/2/hi/science/nature/6170346.stm
OK, back to science! The CLIVAR P16S field campaign has entered the waters of the South Pacific known as a subtropical gyre. Gyre means “circular or spiral motion.” In the ocean, wind generated surface currents travel in a circular direction, either clockwise or counterclockwise, forming a large, circular body of water. The circular direction of the currents is caused by the Coriolis Force acting to deflect motion to the right in the Northern Hemisphere and to the left in the Southern Hemisphere due to the Earth’s rotation. The South Pacific gyre is located in the Southern Hemisphere, so winds and water are deflected to the left. Because of the deflection to the left, the gyre circulates in the counterclockwise direction, forcing water to pile up in the center of the gyre. In the last post, “An Appreciation for True-Color Satellite Imagery” we discussed how microscopic plants, or phytoplankton, require nutrients to grow. Blooms (large cell numbers) of phytoplankton cannot grow in these gyres because the water that piles up within the center of circulation is nutrient deficient.
Global Ocean Circulation
http://oceanmotion.org/html/background/wind-driven-surface.htm
We can use the information about the color of the light being absorbed and reflected by the ocean to deduce the concentration of phytoplankton biomass using the proxy Chlorophyll a. Chlorophyll a is a pigment that both land plants and phytoplankton use to convert light to sugars in their chloroplast. Chlorophyll a absorbs strongly in the blue color of light. So when there is a lot of Chlorophyll a, then the light reflected back includes very little blue light. When there is very little or no Chlorophyll a, then a lot of blue light is reflected back. The figure below is an ocean color image based on the information I just described. The blue color represents little to no Chlorophyll a (or phytoplankton) present while the bright colors of yellow green and red represent increasing concentration of Chlorophyll a or phytoplankton biomass.
SeaWiFS Ocean Color image, Pacific Ocean
http://oceancolor.gsfc.nasa.gov/cgi/image_archive.cgi?c=CHLOROPHYLL
Please bear in mind that this explanation is very simplistic. You can learn more about how ocean color works here.
See the image below for the current cruise track of CLIVAR P16S. They are almost in Tahiti. Just a couple more weeks…
Cruise Track, CLIVAR-P16S
ACKNOWLEDGEMENTS: NASA’s Ocean Ecology Laboratory Field Support Group is participating in the US Repeat Hydrography, P16S field campaign under the auspices of the International Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP). The US Climate Variability and Predictability Program (CLIVAR), NOAA and the NSF sponsor this campaign.
http://oceanservice.noaa.gov/facts/biggestocean.html
http://oceanservice.noaa.gov/facts/pacific.html
http://www.iol.ie/~spice/Indones.htm
http://www.rmg.co.uk/explore/sea-and-ships/facts/faqs/what-and-where-are-the-spice-islands
http://news.bbc.co.uk/2/hi/science/nature/6170346.stm
http://www.merriam-webster.com/dictionary/gyre
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/crls.rxml
http://oceanworld.tamu.edu/students/currents/currents3.htm
http://oceancolor.gsfc.nasa.gov/cgi/image_archive.cgi?c=CHLOROPHYLL
http://oceancolor.gsfc.nasa.gov/SeaWiFS/
We have spent the last few weeks discussing the differences between inherent and apparent optical properties in the ocean and how we measure them. Now let’s take a moment to appreciate the information these data give us. I am sure many of you have seen satellite images of the ocean, hurricanes, etc. on the news and at other outlets. A lot of work goes into each and every one of those images and they can show remarkable things on a global scale that would be difficult to detect through fieldwork alone.
Below you will see a true color image of a phytoplankton bloom in the Barents Sea that was acquired on August 24, 2012 by NASA’s MODIS Aqua satellite . The Barents Sea is part of the Arctic Ocean and is located off the northern coasts of Norway and Russia. The word phytoplankton is Latin for plant (phyto) and to wander or drift (plankton). Phytoplankton can photosynthesize and produce energy from sunlight just like plants do on land. They also take up carbon dioxide and release oxygen like land plants. Phytoplankton are an important component of the food chain as other organisms such as zooplankton and fish use them as a food source. Additionally, they play an important role in the global carbon budget because they can use the carbon (CO2) that is absorbed by the ocean to make sugars.
Barents Sea phytoplankton Bloom
There are many types of phytoplankton that bloom in the ocean including diatoms, dinoflagellates, and coccolithophores, just to name a few. You can learn more about different phytoplankton groups here. They all rely on specific nutrients, such as nitrogen (NO3, NO2, etc.), phosphorous (PO4, etc.) and trace metals (iron, magnesium, etc.). Phytoplankton blooms occur when many individuals, or cells, of one species are present in one region of a body of water (lake, estuary, open ocean), altering the color of the water. In the image above, the water is dominated by a species of coccolithophore. Coccolithophores are a type of phytoplankton that are covered with plates made of calcite called coccoliths. Calcite, or calcium carbonate, is white giving that creamy white look to the water. You can learn more about this coccolithophore bloom here.
This next image was recently featured on NASA’s OceanColor website. It was taken off the western coast of Africa where a current called the Benguela current flows northward bringing water from the South Atlantic and Indian Ocean. In this image from April 10, 2014 we can see a yellow discoloration in the water. I just learned that this area is prone to toxic hydrogen sulfide precipitation events that have been known to cause fish and other marine animal mortalities. Amazingly, these events have been captured using satellite imagery. However, the cause of this particular discoloration has not, as of this post, been determined. This is where fieldwork comes in! Still, it is very cool! Thanks to Norman Kuring at NASA Goddard for locating this feature.
Discoloration in the Benguela Current off the coast of Namibia
You can enjoy many other satellite images at NASA’s Visible Earth website.
References:
http://www.worldatlas.com/aatlas/infopage/barentssea.htm
http://earthobservatory.nasa.gov/Features/Phytoplankton/
http://www.bigelow.org/foodweb/microbe0.html
http://protozoa.uga.edu/portal/coccolithophores.html
http://oceancolor.gsfc.nasa.gov/
http://oceancurrents.rsmas.miami.edu/atlantic/benguela.html
http://oceancolor.gsfc.nasa.gov/cgi/image_archive.cgi?i=423
http://www.sciencedirect.com/science/article/pii/S0967063703001754
ACKNOWLEDGEMENTS: NASA’s Ocean Ecology Laboratory Field Support Group is participating in the US Repeat Hydrography, P16S field campaign under the auspices of the International Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP). The US Climate Variability and Predictability Program (CLIVAR), NOAA and the NSF sponsor this campaign.
One of the greatest tools used by oceanographers today for measuring ocean processes is the CTD. CTD stands for Conductivity, Temperature and Depth. Conductivity is a measure of ocean salinity. The CTD is used to collect profile data in the ocean. The CTD is typically accompanied by a carousel, or rosette, of large bottles (Niskins) that can hold about 10 liters (2.6 U.S. gallons) of water. Some Niskins are large enough to hold 30 liters. These bottles have spring-loaded caps that can be triggered to close at specified depths. The CTD and other sensors, such as a chlorophyll fluorometer, and an Acoustic Doppler Current Profiler (ADCP) that measures current velocities, and other sensors can also be attached within the rosette package.
The whole package is connected to a very long cable and is mechanically lowered by a winch operator down through the water column, which is called the ‘downcast.’ During the downcast, information about salinity, temperature, depth and data from the other sensors are sent to a computer on board the ship. The computer is connected through the cable that is lowering the package. The downcast is halted once the package reaches close to the ocean floor. When the CTD is raised back to the surface, the ‘upcast’, each of the Niskin bottles is closed at assigned depths, collecting water as it travels back to the surface.
Once the Rosette package is back aboard the ship, the scientists are able to collect water from the bottles for their analyses. The parameters collected and analyzed during CLIVAR campaigns includes but are not limited to: salinity, oxygen, nutrients, chlorofluorocarbons (CFCs), dissolved inorganic carbon (DIC), total alkalinity, pH, dissolved organic carbon (DOC), helium, and tritium.
Certain compounds, such as some radionuclide (tritium, carbon-14, etc.) and CFCs, can be used as ‘tracers’. These tracers are used to follow ocean currents and calculate the age of water parcels. CFCs were prominently used in refrigerators and air conditioning units until the 1970s when they were banned over the concern of ozone depletion. You can learn more about the CFC tracer program here. Through the WOCE and CLIVAR programs CFC concentrations have been measured all over the world.
Map of global CFC measurements
http://www.pmel.noaa.gov/cfc/
The measurement of pH, total alkalinity and DIC are important for monitoring ocean acidification. Ocean acidification (OA) is the decrease in ocean pH as a result of an increase in carbon dioxide (CO2) absorption by seawater. OA is a prominent concern in today’s world. CO2 is pumped into the atmosphere from everyday human activities, such as emissions from vehicles and industrial pollution. Each year approximately 25% of the CO2 pumped into the atmosphere is absorbed by the ocean. Although plants can use CO2 for photosynthesis, the increase also has negative implications. As the amount of CO2 absorbed by the increases, the pH is expected to continue decreasing.
pH time series
http://www.pmel.noaa.gov/co2/story/OA+Observations+and+Data
The pH of the ocean directly affects organisms that form calcium carbonate shells or structures, like corals, oysters, clams and sea urchins. An acidic environment causes the calcium carbonate to dissolve and makes it more difficult for the organisms to make their calcium carbonate skeletons. Therefore, it is important that programs like CLIVAR are monitoring global CO2 concentrations (part of the DIC pool), total alkalinity (the ability for the ocean to neutralize acids) and pH. We know that decreases in ocean pH can negatively impact marine organisms. You can see more about the effect of ocean acidification or marine organisms here.
Ocean Acidification
http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F
As I was conducting some research for this blog post I came across this article that was posted at the Earth Observatory in 2008 about the global carbon budget. I thought it was appropriate to bring it back here.
Earth Observatory article from 2008
References:
http://www.whoi.edu/home/oceanus_images/ries/calcification.html
http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F
http://water.me.vccs.edu/exam_prep/alkalinity.html
http://earthobservatory.nasa.gov/Features/OceanCarbon/
http://rspb.royalsocietypublishing.org/content/275/1644/1767.full
ACKNOWLEDGEMENTS: NASA’s Ocean Ecology Laboratory Field Support Group is participating in the US Repeat Hydrography, P16S field campaign under the auspices of the International Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP). The US Climate Variability and Predictability Program (CLIVAR), NOAA and the NSF sponsor this campaign.
The NASA FSG folks and the rest of the science crew on the US Repeat Hydrography P16S field campaign have experienced some weather delays, which can be expected when working the Southern Ocean close in time to the Southern Hemisphere winter. They encountered 45-knot winds (~51 miles per hour) sitting on top of their planned sampling area at around 60 degrees South latitude. For the safety of all they could not conduct science under those conditions. So they traveled ~200 miles north to escape the weather and then returned southward once the weather had settled. Below you will see some freeze frame clips from the movie Joaquin Chaves captured showing the large swells and the dramatic gray skies of the Southern Ocean. The movie was recorded through the porthole, safe inside the ship.
Stormy weather 1
Stormy weather 2
Stormy weather 3
Stormy weather 4
In spite of the rough weather, the FSG fellows have taken advantage of some calmer days to deploy a radiometer. A radiometer measures apparent optical properties or AOPs. You might recall from Blog #2 that we discussed Inherent Optical Properties or IOPS that characterize the absorption and scattering (reflecting) of light by dissolved and particulate materials in the water. The measurement of IOPs can be done at any time day or night. AOPs on the other hand must be measured during the daytime, preferable when there are clear skies and the sun is directly overhead. AOPs describe how the light is entering and exiting the water column. Remember that sunlight contains a whole spectrum of colors that are determined by their wavelength. We see what is called the “visible spectrum” like what is in the image below.
As the sunlight penetrates the water column, some of the light is absorbed, some is scattered (reflected) backward toward the sky and the rest is scattered forward into the depths of the ocean. Water itself absorbs most of the red light, so we never really see a red ocean (unless there is something unusual in the water).
The character of the light that is reflected back out of the water can be different than what went in. More specifically, the wavelengths or colors that are reflected back out are the colors that were not absorbed or scattered forward. Think about when you are at the beach, say Ocean City, MD or Rehoboth Beach, Delaware. The water typically looks brown or green, right? This is because particles, including both algae and sediment (and water), are absorbing all of the blue and red light, and the leftover colors of brown and green are reflected back out. Conversely, for those of you who have seen blue water in places like the Caribbean or around Bermuda, the circumstances are different. There are very few particles or phytoplankton in the water to absorb the blue light like in the coastal water. Therefore, that blue color is reflected back out , which is why the water looks so blue and pretty. A radiometer that the FSG is deploying on this field campaign measures the colors and amount of the light entering and exiting the water column. The radiometer is hand deployed and, I can tell you, it’s a lot of work!
Joaquin and Scott preparing to deploy the radiometer
Photo credit: Isabella Rosso
Dropping the radiometer into the water
Photo credit: Scott Freeman
Joaquin guiding the cable; Photo credit Isabella Rosso
Mike pulling the radiometer back to the surface
Satellite instruments, such as SeaWiFS (no longer operational) and MODIS-Aqua (operational) measures this light just like the radiometer so that we can get beautiful images that you can see below.
True color image of Chesapeake Bay
http://oceancolor.gsfc.nasa.gov
True color image of Hawaii
http://oceancolor.gsfc.nasa.gov
Our FSG fellas are working very hard during this field campaign. But every now and then you need to have a little fun. Mike Novak sent this picture of a snowman that was built on the bow of the ship. I think the eyes, nose, and buttons are raisins.
References:
http://ushydro.ucsd.edu/p16s-weekly-reports/
http://www.oceanopticsbook.info/
http://oceancolor.gsfc.nasa.gov
ACKNOWLEDGEMENTS: NASA’s Ocean Ecology Laboratory Field Support Group is participating in the US Repeat Hydrography, P16S field campaign under the auspices of the International Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP). The US Climate Variability and Predictability Program (CLIVAR), NOAA and the NSF sponsor this campaign.
As many of you probably heard, there was an 8.2-magnitude earthquake off the coast of Northern Chile on Tuesday night. As with any earthquake around a coastal region or on the ocean floor, there is great concern about the formation of a tsunami. A Tsunami is series of waves with a very large wavelength. Think of a series of waves hitting a beach. The distance between each wave hitting the shore is the wavelength. Now picture a wavelength that is 100s of miles long! Because the wavelengths are so long, the waves travel at very high speeds, around 600 miles per hour, in the deep ocean. This is the speed at which a commercial jet plane travels! However, the wave height (the height from the base of the wave at the water line to the top of the wave) is very small, maybe a few feet tall. As you can imagine, a boat or ship in the open ocean wouldn’t even notice such a tiny wave.
Below is a screen shot from a CNN video report about the earthquake. In this video you can see how the waves propagate out from the source of the earthquake out into the ocean (red arrow).
Wave propagation
http://www.cnn.com/2014/04/01/world/americas/chile-earthquake/
The story changes, however, when the depth of the ocean decreases, such as when approaching land. All of that energy in that fast wave gets slowed down and subsequently the height of the wave gets bigger, and sea level near shore can rise at least 50 feet! Thankfully, our colleagues are out of harms way from tsunamis because they are in the middle of the deep, open ocean.
The ship and its inhabitants ARE, however, subject to waves that are created by storms and strong winds. Joaquin made a video of the wave action that you can see below. Here are some freeze frame ‘action shots’ from the video.
https://www.youtube.com/watch?v=cBTORY0aalE&feature=youtu.be
Stage 1
Stage 2
Stage 3
Stage 4
And, lastly, I thought it would be good to show some pictures of how cold it is that far south and how challenging it can be to work outside on deck in the cold. In this picture you can see icicles hanging off the ship during recovery of an IOP package deployment.
Water intrusion during recovery of the IOP package
Mike and Scott are having a conversation as they wait for the IOP package to return to the surface of the ocean. I wonder what they are talking about???
A very intense conversation ensues while waiting for the IOP package to return to the ocean surface
You can watch an entire IOP deployment below.
Lastly, when working so close to the continent of Antarctica, there must be a sighting of an iceberg.
Iceberg!
Sources:
http://www.nws.noaa.gov/om/brochures/tsunami.htm
http://www.cnn.com/2014/04/01/world/americas/chile-earthquake/
