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Click below to go to the Cruise Logs - (photo credit: Lophelia Coral - Open-File Report 2008-1148 & OCS Study MMS 2008-015)

DISCOVRE 2009



Cruise Log: 8/11/2009    



River in the Sea

Liz Baird

"There is a river in the ocean. In the severest droughts it never fails and in the mightiest floods it never overflows; its banks and bottom are of cold water, while its current is of warm, the Gulf of Mexico is its fountain, and its mouth is the Arctic Sea." Matthew Fontaine Maury, "The Physical Geography of the Sea and Its Meteorology" 1855

It is difficult to capture the blue of the water out here. (photo credit Art Howard) - click to enlarge
It is difficult to capture the blue of the water out here. (photo credit Art Howard) - click to enlarge
The water out here is blue - a mesmerizing deep delicious blue that makes many of us envious of the sub crew member who gets to jump overboard with the line for retrieving the submersible. The blue is an indicator of clean water with little sediment or microscopic plant and animal life suspended within it. It is like the color of glacial water, trapped above the frozen river of ice. But with each swell, the water rises and falls, almost like some ancient enormous beast breathing. When we look over the side, the sunlight penetrates deeply, creating shafts of light that dance as starbursts when the ship moves forward.

We are off Cape Canaveral in the Florida Current, which is sometimes called the beginning of the Gulf Stream. This warm water (usually above 80° F) moves northward towards Cape Hatteras, NC. Matthew Fonatine Maury described it in 1855:
      "Its waters, as far from the Gulf as the Carolina coasts, are of an indigo blue. They are so distinctly marked that their line of junction with the common sea-water may be traced by the eye."

This water is moving northward, carrying warmth from near the equator towards the Arctic. The warm surface temperature is as noticeable as the color. In the 15th century John Cabot noticed that beer stored in the hold of the wooden sailing ship got warm and went bad in the Gulf Stream. Ben Franklin became interested in locating the Gulf Stream as a way of improving the mail service to Europe. He started using thermometers to measure the water temperature and recorded the information over several voyages. His nephew, Jonathan Williams, inherited this interest and went on to publish "Thermometrical Navigation" in 1799 which identified the Gulf Stream for mariners.

Ironically, we still use temperature to help map the flow of this constantly shifting stream of water, but now, instead of lowering a bucket over the side and inserting a thermometer, we use satellites with infrared sensors to produce images of the ocean. This mapping is important because the stream moves constantly, with eddies of water spiraling off. At Cape Hatteras, the Gulf Stream has a speed of 4 knots down to about 1,000 feet. This current transports more than 2 billion cubic feet of water every second - more than 500 times the capacity of the Amazon.

Using the submersible, however, we descend greater than 1,000 feet. In these depths we know the water will be cold - quite cold, but we can't always predict the current. The Microlander launched and recovered by Murray Roberts (SAMS) collected some of the only continuous data we have about the current in the deepwater coral habitats. When we know more about the current at the bottom, we will begin to understand the dispersal and feeding strategies of deepwater organisms such as Lophelia coral. Dr. Cheryl Morrison (USGS) has been collecting data on the genetics of the deepwater corals. The distribution of different populations can suggest the direction of the current. After every sub dive she takes small samples of the coral tissue to analyze back at her lab. An understanding of the larval biology and timing of spawning along with genetic data will help make a more accurate prediction of the current flow. Understanding the current also allows us to develop a model of how food (energy) moves through the system. The corals are fixed to the bottom, and are dependent upon the current to bring their food past their polyps.

The incredible blue of these warm waters has been known for centuries. It is only recently that we have begun to understand the cold environment of these deep water habitats below the Gulf Stream.

Background information for this was found in "The Gulf Stream: Tiny Plankton, Giant Bluefin, and the Amazing Story of the Powerful River in the Atlantic" by Stan Ulanski published by the University of North Carolina Press, Chapel Hill, 2008.



New sites - New information - New ideas

Dr. Martha Nizinski

Martha Nizinski (NOAA) processing some of the samples collected by the Johnson-Sea-Link submersible. (photo credit Liz Baird) - click to enlarge
Martha Nizinski (NOAA) processing some of the samples collected by the Johnson-Sea-Link submersible. (photo credit Liz Baird) - click to enlarge
After several days at sea we have fallen into a "normal" sampling routine. The weather has been perfect for sampling and we have been fortunate to collect samples for all the projects represented on this cruise.

I have made two dives in the submersible, both at the same location. We had not visited this deep (approximately 800-900 m), offshore site before and, based on images produced by the echosounder, this area looked promising as deepwater coral habitat. What we encountered was a habitat that was very different from what we have seen previously in this area. The bottom appears to be hard substrate covered with a layer of sediment. There are areas of dead coral, sometimes with live colonies of hard corals growing on the surface of the structure, especially on the top. The habitat here is rather sparse, with the fauna dominated by sessile invertebrates such as sponges, gorgonians and other corals. These animals tend to occur in small patches or singly. Surprisingly, the dominant hard coral in this area is not Lophelia pertusa, but rather Enallopsammia profunda. We have seen Enallopsammia before in this region, but never as the dominant hard coral. One other surprising observation from this area is the lack of large mobile animals; no large crustaceans have been observed here. The diversity and abundance of fishes and echinoderms have also been low.

In contrast to this offshore, deeper site is a shallower (400 m) more inshore site that was sampled on Day 1 of our expedition. This first dive of the trip turned out to be very important since data collected here will provide information we can use for comparison with several of our other sampling sites. For example, we can compare habitat information and diversity of species between these inshore and offshore sites since the dive locations are approximately at the same latitude. Additionally, we can compare this inshore site with some of our sites off North Carolina and Vioska Knoll in the Gulf of Mexico since they are approximately at the same depth. Information collected during this cruise will be beneficial to help us better understand site-specific patterns of diversity and community structure as well as how diversity and abundance of species varies with depth and latitude. All the data we are collecting help us make progress toward understanding the patterns we observe. The next step is to use this information to formulate hypotheses about the processes behind the patterns.



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