NOAA Teacher at Sea
Aboard NOAA Ship Ronald H. Brown
February 15 – March 5, 2012
Mission: Western Boundary Time Series
Geographical Area: Sub-Tropical Atlantic, off the Coast of the Bahamas
Date: February 17, 2012
Weather Data from the Bridge
Position: Windspeed: 15 knots
Wind Direction: South/Southeast
Air Temperature: 23.9 deg C/75 deg F
Water Temperature: 24.5 deg C/76 deg F
Atm Pressure: 1016.23 mb
Water Depth: 4625 meters/15,174 feet
Cloud Cover: less than 20%
Cloud Type: Cumulus
Sailors used to describe their trips as short-haul or coastal,
or “long seas” which also was described as going “Blue Water”
We are off to a great start after passing the harbor lighthouse and breakwater, and the seas are calm and winds gentle. The Low Country and barrier islands of South Carolina disappear quickly over the horizon, and the most striking change for me is the color of the water. As we have transited from the sediment rich waters upriver, to the estuary, and out to the ocean, its color has gone from grayish, to green to blue.
- Bay/Estuary water in Charleston
Gulf Stream water
As a rapid indicator of what’s going on within it biologically, oceanographers use the color of the water. To quantify their observations for other scientist to compare results, a white secchi disc is lowered just below the surface and the observer compares the ocean’s color with tinted water in a series of small vials – the Forel-Ule Scale. (Francois Forel was an oceanographer and his end of the scale is the bluest; and Willi Ule was a limnologist and his end of the scale is darker, reflecting the fresh waters he studied.) The 21 colors run the gambit of colors found in natural waters and modified by the plankton community and range from brownish-to-green-to-blue. This gives you a quick measure of productivity of the waters and the types of phytoplankton predominating. For example: Diatom blooms are brownish and Dinoflagellate blooms form the notorious red tides. Clear, less productive waters look blue, and we are sailing into waters that are a deeper blue with every league we sail.
I lack a secchi disk and we can’t stop the ship to lower one anyway, so I am using instead a scupper on the side as a photographic frame to document this well-studied and interesting phenomenon.
“Being on a boat that’s moving through the water, it’s so clear.
Everything falls into place in terms of what’s important, and what’s not.”
Before departing on the trip I came across Richard Pough’s bird map of the Atlantic. On it he divides the ocean into 10-degree quadrants and indicates the average water temperature and number of birds he sighted daily. The good news is we are heading southeast into warmer waters. The bad news is, he does not indicate a very productive hunting ground for bird watching. For example, Cape Hatteras, NC, where the Gulf Stream skirts North Carolina, shows 40 birds. Off the highly productive sub-polar regions like Iceland where there are great breeding colonies of seabirds like gannets, he indicates scores of birds. Regardless, I am hopeful we will find some true seabirds to photograph on our voyage; and perhaps have some migrating songbirds drop in for a rest.
Gulf Stream sunset
Today, as our colleague Wes Struble discusses on his blog, we retrieved our first samples with the CTD rosette. Water is retrieved from predetermined levels between the surface and 4,500 meters sealed in bottles for salinity and dissolved oxygen analysis. These two physical features, along with temperature, are the benchmarks physical oceanographers rely upon to track the ocean circulation.
For an understanding of this process and an overview of the project, I met with Molly Baringer in her office – a large bench that the ship’s carpenter built on deck. It seats three and is similar to a lifeguard stand, so it can give a view of the water and fit over the [dis]array of equipment constantly being shifted around the fantail by various scientists and deck hands. With the calm seas and sunny weather, it is the perfect spot on the ship to sit with a laptop to outline daily assignments for all of us, review the mass of data streaming in, and relax to watch the sunset.
“When I am playful,
I use the meridians of longitude and parallels of latitude for a seine,
and drag the Atlantic Ocean for whales!”
Scientists and crew prepare to retrieve a mooring before the next big wave!
Chief scientist Dr. Baringer is a physical oceanographer and so is interested less in the creatures moving around in the ocean and more about the water currents that are moving them around, and particularly the vast amount of heat that is transferred from the Equator to the Polar Regions by “rivers in the sea” like the Gulf Stream.
Currents and storms in our atmosphere produce our daily weather patterns, which of course change seasonally too. Ocean currents work on a much longer time scale and the text book example of the turnover time of warm water moving Pole-ward, cooling and returning to the Tropics as “centuries.” This timeframe infers that dramatic fluctuations in climate do not occur.
However, by analyzing ice cores from Greenland, scientists recently have detected evidence of abrupt changes in climate – particularly a significant cooling event 8,200 years ago – that could be associated with vacillations in the Gulf Stream. Although lacking a blackboard at her impromptu lecture hall on deck, a patient Dr. Baringer was artful in walking me through a semester of climatology and modeling to highlight the implications of an oscillating Gulf Stream and its deepwater return waters – the Deep Western Boundary Current.
Surface water is driven from the southern latitudes towards the Poles along the western side of the Atlantic, constantly deflected in a clockwise pattern by the Earth’s rotation. Bathing Iceland with warm and saltier water and keeping it unusually mild for its sub-polar latitude, the Gulf Stream divides here with some water flowing into the Arctic Sea and the rest swirling down the Eastern Atlantic moderating the climate in Great Britain, France and Portugal. (This explains the presence of a rugged little palm tree that I once saw growing in a Scottish garden.)
Perturbations in the northward flow of heat by meanderings of the Gulf Stream or the smothering of it of it by lighter fresh waters from melting ice in Greenland and Canada appears play a significant role in occasionally upsetting Europe’s relatively mild and stable climate – which is bad enough. What is more alarming is new evidence that these changes don’t necessarily occur gradually over centuries as once assumed, but can take place rapidly, perhaps over decades.
There is more bad news. The surface of the sea is dynamic and even without wind and waves, there are gentle hills and valleys between areas. I remember my surprise when our physical oceanography teacher, Richard Hires, pointed out that because of warmer water and displacement by the Earth’s rotation, Gulf Stream waters are about a meter higher than the surrounding ocean…that to sail East into it from New Jersey, we are actually going uphill. If these giant boundary currents are suppressed in their movements, it will exasperate an ongoing coastal problem as those hills and valleys of water flatten, resulting in rising sea levels and erosion along northern coastlines.
This explains why we are “line sailing” at 26.5 North, sampling water and monitoring sensors arrayed on the parallel of latitude between Africa and the Bahamas. To measure change, it is necessary to have baseline data, and the stretch of the Atlantic is the best place to collect it.
Snap shots of the water column are taken using the CTD apparatus as we sail an East-West transect, but at $30-50,000. Per day for vessel time, this is not practical or affordable. Here is where moorings, data recorders and long-life Lithium batteries come into play. By anchoring a line of sensors in strategic locations and at critical depths to take hourly readings, year-long data sets can be recorded and retrieved periodically. Not only does this save time and money, it is the only way to generate the ocean of data for researchers to analyze and create a model of what is happening over such a vast region – and what may occur in the future.
For more specific details, check out the project overview.
|Deep Western Boundary Current Transport Time Series to study:
-the dynamics and variability of ocean currents;
-the redistribution of heat, salt and momentum through the oceans;
-the interactions between oceans, climate, and coastal environments; and
-the influence of climate changes and of the ocean on extreme weather events.
Information at: http://www.aoml.noaa.gov/phod/wbts/ies/index.php
We hear that “The package is on deck” and it is time to collect water samples from the 24 different depths the Niskin bottles were fired (Remotely closed). As any aquarist will assure you, as soon as seawater is contained it begins to change, so we always start with the bottom water and work around to the top water since dissolved oxygen levels can drop with rising temperatures and biological activity from planktonic creatures trapped along with the water samples.
Although as oceanography students we read that most ocean water is quite cold (~3.5C) because only the top 100 meters soaks up the warmth from sunlight, it is still an awakening for me to fill the sample bottles with even colder bottom water. After a half hour of rinsing and filling bottles, my hands are reminded of the times I worked in an ice cream parlor restocking containers from the freezer and filling soft-serve cones. It is a delight to get to the last several bottles of warm (25C) surface water.
Once the DO and salinity bottles are filled, they are removed to the chemistry lab and the Niskins are all mine. By holding a small plankton net under them as they drain excess water, I try my luck at catching whatever has almost settled to the bottom. There is an extra bonus too. A patch of floating Sargassum weed that tangled in the rosette was retrieved by the technician and set aside for me to inspect.
Windrows of Sargassum weed drift past the Ron Brown
Here is what I found under the microscope so far:
The bottom water is absolutely clear with no obvious life forms swimming around. However a magnification of 50x’s and the extra zoom of my handy digital camera set-up reveals a number of things of interest I am sorting into AB&C’s:
Abiotic: Specks of clear mineral crystals. Are these minute sediments washed from the mainland or nearby Caribbean islands? Or is it possible they are quartz grains carried from much greater distances, like the Saharan dust that satellite images have proven are swept up by desert winds and carried all the way across the Atlantic?
Biotic: Although I can not find anything living, the silica dioxide skeletons (frustules) of at least two species of diatoms are present. These fragile fragments of glass accumulate in deep sediments below highly productive zones in the sea and different species are useful to paleontologists for determining the age of those deposits. On land, fossil diatom deposits are mined for diatomaceous earth – used as an abrasive and cleaner, pool filter material, and even in nanotechnologyresearch applications. There is other detrital material in the samples, but nothing identifiable.
Celestial(?): One tiny round particle caught my attention under the microscope. It looks like the images I’ve seen of microtektites – glassy and metallic meteor particles that have been molded by the heat of entry into the atmosphere. The Draxler brothers, two science students in Massachusetts, collect them and I hope they will confirm my identification when I see them again.
Dust particle (Right) and foraminifera (Center)
From the surface:
The warm, sunlit surface water here is covered with Sargassum weed, a curious algae that sustains an entire ecosystem in the waters mariners named the Sargasso Sea. On board the Brown it is simply called “weed” in part because it can be a minor nuisance when entangled with equipment. The Sargassum’s air bladders that support it at the surface reminded Portuguese sailors of their sargazagrapes and they named the gulfweed after them.
Can you spot the two Sargassum shrimp next to the air bladder?
Floating Sargassum weed harbors a great variety of other creatures including baby sea turtles, crustaceans and especially bryozoan colonies. The film of life encrusting the weed is sometimes called aufwuchs by scientists and is a combined garden and zoo.
A quick rinse in a plastic bag revealed two species of bryozoan and numerous tiny crustaceans. The Phylum Bryozoa is the “moss animals” a puzzling colonial creature to early biologists. Bryozoans are an ancient group with a long fossil record and are used by paleontologists as an “index” species to date sediments.
To my delight there were also some foraminifera in the samples. “Forams” as they are called by researchers, are single celled protozoa with calcium carbonate skeletons. They are abundant and widespread in the sea; having had 330 million years to adjust to different habitats – drifting on the surface in the plankton community and on benthic habitats on the bottom.
It is not necessary for you to go to sea with a microscope to find them. I have seen their skeletons imbedded in the exterior walls of government buildings in Washington, DC; and our own lab building at Sandy Hook, NJ has window sills cut from Indiana limestone – formed at the bottom of the warm Mesozoic seas that once covered the Midwest. In the stone, a magnifying glass reveals pin-head sized forams cemented among a sea of Bryozoan fragments. Some living forams from tropical lagoons are large enough to be seen without a magnifier, and are among the largest single-celled creatures on the planet. With a drop of acid (The acid test!) our Geology students confirm that our window sills are indeed made of limestone as the drops fizzing reaction releases carbon dioxide sequestered when the animal shell formed.
Living foraminifera eat algae, bacteria and detritus and are fed upon by fishes, crustaceans and mollusks. Dead forams make contributions to us by carrying the carbon in their skeletons to the bottom where it is sequestered for long geological periods.
Geologists also use different species of forams as “index” species to fix the date of strata in sediment cores and rocks. The appearance and demise of their different fossil assemblages leave a systematic record of stability and change in the environment; and paleoclimatologists use the ratios of Carbon and Oxygen isotopes in their skeletons document past temperature ranges.
Our first plankton samples extracted from the deepest samples retrieved from the Niskin bottles at 4,000 meters (2.5C) did not produce any forams. This may be because in deep, cold water, calcium carbonate is more soluble and the skeletons dissolve. Presumably why we identified only the glassy tests of diatoms.
Foraminifera shell at 100x’s
Tiny Paramecia swarm over the detritus in my slide and taking a closer look at that and the growth associated with the weed I am reminded of Jonathon Swifts jingle:
Big fleas have little fleas
Upon their backs to bite ‘em
And little fleas have lesser fleas
And so, ad infinitum
Sunset over the Sargassum Sea
The Chief Scientist:
A day in the life of our chief scientist involves: checking with her staff to evaluate the previous day’s collections, consulting with visiting scientists on their needs and any problems that might arise, checking with the deck hands and technicians about equipment needs and repairs, advising the ship’s officers of any issues, and making certain we are on course and schedule for the next station.
And then rest? Hardly!
Even when off duty there are inquiries to field from staff, scientists and crew; equipment repairs to be made; and software that needs to be tweaked to keep the data flowing.
How does one prepare for a career like this?
Physically: the capacity to function on little sleep so you can work 12-hour shifts and be on-call the other twelve. (And there is little escape at mealtimes either, where the conversation never stays far from the progress of the cruise.)Mentally: the capability to multi-task with a variety of very different chores.
Emotionally: the flexibility to accommodate people with many different personalities and needs, while staying focused on your own work.
Also, excellent organizational skills, since months of planning and preparation are crucial.
And perhaps most importantly, a sense of humor!
Chief Scientist Dr. Molly Baringer prepares to fire the XBT
off the stern for an 800 meter profile of temperature and pressure.