Temperature (along with salinity) affects the density and thus the stability of the water column. This in turn profoundly affects many biological processes in the upper ocean. Warmer water is less dense and thus tends to stay on top of colder water. During winter, storm winds mix the water column, and the temperature is nearly uniform in the top several hundred meters. As spring approaches, increasing solar radiation warms the surface waters and this warmer, buoyant water stays on top. This increases the stability of the water column, preventing deeper, nutrient-rich water from being mixed into the surface from below. The stable surface layer keeps the phytoplankton near the surface where there is plenty of light, plus plenty of nutrients brought to the surface by winter mixing. This combination of conditions allows the organisms to grow rapidly, and a spring bloom occurs.
Many organisms are also adapted to live at different temperatures; thus the temperature of the water can determine the diversity or numbers of organisms living there. As temperature changes with season and location, the diversity and numbers of organisms can change as well.
Temperature data is collected with theCTD. CTD stands for Conductivity, Temperature, and Depth recorder. It is an electronic instrument that continuously records the salinity (by measuring conductivity), temperature, and depth (by measuring pressure) as the instrument is lowered on a hydrowire from a ship. The temperature is instantly recorded from the surface to depth, and gives a profile of temperature and how it changes throughout the water column. (Return to top) Salinity
Salinity refers to the saltiness of the water. Salinity (along with temperature) affects the density and thus stability of the water column. This in turn profoundly affects many biological processes in the upper ocean. Saltier water is more dense and thus tends to sink below fresher water. Oceanographers can identify where a water mass comes from just by noting its salt content and temperature.
Salinity data is collected with theCTD. CTD stands for Conductivity, Temperature, and Depth recorder. It is an electronic instrument that continuously records the salinity (by measuring conductivity), temperature, and depth (by measuring pressure) as the instrument is lowered on a hydrowire from a ship. The CTD continually records salinity from the surface to depth, and gives a profile of salinity and how it changes throughout the water column. BATS technicians also analyze the salinity of water collected from the CTD once it is back onboard ship. They make this measurement on a salinometer. This machine measures the salt content of the water directly, rather than by measuring the water's conductivity. (Return to top) Depth
The ocean at the BATS site is more than 4 kilometers deep! Ocean depth is measured using an echo sounder and an electronic instrument called the CTD. CTD stands for Conductivity, Temperature, and Depth recorder. The CTD continuously records the depth by measuring changes in water pressure as the instrument is lowered on a hydrowire from a ship. The deeper the water, the higher the pressure. Depth measurements provide a framework that helps makes sense of the other measurements made at BATS. When an ocean property is plotted as a function of depth, the resulting graph is called a profile. For instance, plotting changes in temperature with depth produces a temperature profile of the ocean. Most of the BATS data is in the form of profiles. (Return to top) Oxygen
All animal life in the ocean, from bacteria to zooplankton to fish, requires oxygen to live. Oxygen enters the ocean in two main ways. It diffuses into the ocean surface from the atmosphere, and it is produced by plants in the sea during photosynthesis. The amount of oxygen in the water is controlled by the temperature, as well as by the levels of animal respiration and plant photosynthesis. Oceanographers can use oxygen measurements to determine rates of photosynthesis and animal respiration in the sea on a large scale.
Oxygen data are collected by sensors on theCTD and by analyzing water samples collected with the CTD rosette. Since oxygen is a gas that can easily escape from sea water, it is the first element that BATS technicians sample when the CTD is brought back onboard the ship. The technicians measure oxygen levels by adding chemicals that bind to the oxygen molecules. They can then use an oxygen titrator to determine the amount of oxygen in each sample. (Return to top) Carbon Dioxide
Humans add carbon dioxide to the atmosphere by burning fossil fuels. Carbon dioxide is a greenhouse gas that diffuses into the ocean surface from the atmosphere, and is taken up by plants in the sea during photosynthesis. Because the magnitude of the greenhouse effect depends on the amount of carbon dioxide in the atmosphere, scientists are greatly interested in how much carbon dioxide the oceans can take up from the atmosphere. Uptake of carbon dioxide by the oceans is affected by the temperature of the water (colder water holds more gas) and by the abundance of plants. Plants absorb carbon dioxide during photosynthesis. Oceanographers at BATS are interested in carbon dioxide levels in the sea and how and if they are changing through time.
BATS technicians sample carbon dioxide in much the same way they sample oxygen (as it is also a gas). They then analyze the samples on a machine that traps the gas and measures the amount in the sample by titration. (Return to top) Nutrients
Just like plants in your garden, plants in the ocean require nutrients to grow. The most important nutrients for phytoplankton growth in the ocean are nitrate and phosphate. Some types of phytoplankton, called diatoms, also require the nutrient silicate, which they use to build their cell walls. Some "micro-nutrients" are needed too, but in smaller amounts. Iron is an important micronutrient.
Nutrients are present in a dissolved form in seawater. Plants in the surface waters of the ocean take up these dissolved nutrients during photosynthesis. Once taken up by a plant we say the nutrients are in particle form. When the plants die they are decomposed by marine bacteria. This returns the nutrients to a dissolved form that the plants can once more use. The plants may also be eaten by zooplankton, which digest the plants and also return the nutrients to a dissolved state.
Because light only penetrates a few hundred meters into the sea, no plants grow in the ocean's permanently dark depths. Thus there are no plants in these regions to remove nutrients from the water, and the ocean's deeper waters tend to be enriched in nutrients compared to its surface waters. A phenomenon called upwelling brings nutrients from the ocean depths to the sunlit surface waters where they can be used by plants. In some areas of the world's oceans (like the Sargasso Sea) nutrients are not replenished continually, and plants can sometimes use them up completely. These regions thus become nutrient-poor "ocean deserts" during certain seasons of the year.
Nutrients are measured by collecting water at different depths in bottles on the CTD. They are then analyzed in the onshore laboratory with a nutrient analyzer. This machine adds chemicals that turn the water blue when they bind to nutrients. The darker the blue, the more nutrients in the water. The machine measures the intensity of the color and compares it to a standard curve to determine the amount of nutrient in the sample. (Return to top) Dissolved Organic Carbon (DOC)
In order to completely understand the carbon cycle in the sea, it is important to understand changes in the amount of dissolved organic carbon (DOC). DOC is an important source of nutrition for marine bacteria. Most of the organic carbon in the sea is in a dissolved form.
BATS technicians collect water samples for DOC analysis at different depths in bottles on the CTD. They analyze these samples using a machine that oxidizes the DOC to carbon dioxide gas. They then measure the levels of carbon dioxide in the sample. (Return to top) Particulate Organic Carbon and Nitrogen (POC/PON)
Sea water contains many floating and sinking particles. Collectively, these tiny particles contain large amounts of carbon and nitrogen. Thus in order to completely understand the carbon and nitrogen cycles in the sea, it is important to understand changes in the amount of particulate organic carbon (POC) and particulate organic nitrogen (PON).
Water samples for POC/PON analysis are collected at different depths in bottles on the CTD. BATS technicians filter the particles from the water and analyze them using a machine that combusts the POC to carbon dioxide gas (CO2), and the PON to nitrogen gas (N2). The technicians then measure the amounts of these gases. (Return to top) Phytoplankton Pigments
Phytoplankton are the primary producers in the sea and form the base of the marine food chain. Thus it is important to know how abundant these plants are and what species are present. All plants, on land or in the sea, contain the pigment Chlorophyll a. They use this pigment for photosynthesis. The amount of Chl a pigment in sea water is related to the amount of plant material and is thus used to measure plant biomass in the ocean.
Most phytoplankton also contain what are called accessory pigments. These are different-colored pigments that are able to "harvest" light for photosynthesis at wavelengths that differ from the wavelengths used by Chl a. Many of these accessory pigments are specific to a group of phytoplankton. Thus, instead of collecting phytoplankton cells directly and counting the different kinds (which can be time-consuming and tedious work), scientists can instead measure the relative amounts of the different types of pigments in a water sample. This indicates the major groups of plants that are present in the seawater.
BATS technicians measure phytoplankton Chl a by using fluorescence. They filter water samples and collect the phytoplankton on the filters. They then extract the pigments from the phytoplankton and place them in a machine called a fluorometer. The fluorometer shines light of a certain wavelength (blue) on the pigment sample and the Chl a in the sample fluoresces back at a different wavelength (red). The amount of fluorescence in a water sample is proportional to the amount of Chl a.
Phytoplankton accessory pigments are measured using a High Performance Liquid Chromatography (HPLC) machine. This machine separates the pigments from a water sample and gives a relative measure of the groups of plants that are present in the water.
Bacteria are extremely important in the sea. They play a part in every nutrient cycle in the ocean, and, like the fungi on land, are the primary decomposers. Thus oceanographers are interested in bacteria abundance and in how fast they grow and reproduce.
BATS technicians measure bacteria abundance by collecting water at different depths with the CTD, then filtering the water on filters with tiny pore sizes. Most bacteria in the sea are only about 1/1000 mm in diameter, so a tiny pore size is needed to collect them. The technicians add a stain to the filters that colors the bacteria, making the bacteria easier to count using a high-power microscope designed specifically for this purpose.(Return to top)