Perhaps no program demonstrates the importance of Bermuda's location for marine research better than BIOS's long-term effort to understand climate variability. The keys to this effort are Hydrostation "S," begun in 1954 at a site 12 miles from Bermuda and considered the longest continuous, year-round record of measurements of any spot in the open ocean; and its sister site, the Bermuda Atlantic Time-series Study (BATS). These programs monitor the changes of the physics, chemistry and biology of the ocean surrounding Bermuda, and over time are yielding new insights about ocean variability.

People are naturally curious about the weather. It affects us all, whether we wake up to a fresh foot of new snow in the mountains of Colorado, or tune in to the Weather Channel during hurricane season as another storm brews in the tropics. Weather reflects a constantly changing set of conditions, such as temperature, precipitation and winds, over hours, days or weeks.

Climate, on the other hand, is the broad composite of average weather conditions for a specific region over longer periods, from years to centuries to millennia. Climate can also refer to the "mean" state of the entire planet or to particular regions, such as continents or oceans.

Perceptions about climate have changed as we use a vast array of new technologies to learn more about the planet. For example, we now can predict reasonably accurately whether an El Niño-Southern Oscillation is beginning or waning. The underlying cause of an El Niño event is a warming of water in the tropical region of the eastern Pacific Ocean. This temperature rise alters the pattern of ocean and atmospheric currents, which in turn alters weather patterns regionally and globally. Some regions become warmer and wetter, others colder and drier during an El Niño event. Another pattern of climate variability, the North Atlantic Oscillation (NAO), has brought warmer, wetter and stormier winter weather across much of northern Europe over the last decade.

Gathering information about and understanding the underlying causes of these climate phenomena has growing importance, since both El Niño and NAO profoundly affect human activities and the global economy, for example the agricultural and fisheries industries.
 

As we learn more about climate, it has become increasingly clear that there is a complex interaction or "dance" between the ocean and the atmosphere which influences climate variability. While studying climate of the continents is aided by thousands of monitoring stations across the globe that constantly record each day's weather, our ability to understand the physical interactions between ocean and atmosphere is hindered by the relatively fewer amounts of data collected for the oceans. Long-term ocean observations are thus inordinately important for understanding the relationships between the ocean and atmosphere, and the response of the ocean's circulation and biology to climate variability.

Recent studies by BIOS researchers indicate that the physics and biology of the northwest Atlantic Ocean respond to climate variability such as NAO. For example, surface ocean temperatures cool, mixed layers deepen and rates of photosynthesis for marine plants increase during the so-called NAO negative phase, which last occurred in 1996. This happens in response to winter storms being pushed further out across the seas surrounding Bermuda, rather than to the northwest toward Iceland. Studies we are conducting with Dr. Niki Gruber of the University of California at Los Angeles indicate that the physics and biology of the entire North Atlantic Ocean respond in a coordinated way to climate variability such as NAO.

Climate variability also plays a role in affecting the global balance between the uptake of atmospheric carbon dioxide (CO₂) by the ocean or release of CO₂ to the atmosphere from the ocean. During the last decade, coinciding with a long-term change in NAO, the Sargasso Sea near Bermuda has absorbed an extra 0.6 to 2.8 gigatonnes of CO₂ compared to the 1970's and 1980's. This represents a large change in the ocean storage of CO₂ that has been released to the atmosphere by human activities. Without BIOS's long-term observations at BATS and Hydrostation "S" we could not have shown this profound change in the global carbon cycle.