Earth Gauge » Oceans

Climate Fact: AMO and THC

administrator — Wed, 08 Oct 2008 21:31:36 +0000

The Atlantic Multidecadal Oscillation (AMO), or the North Atlantic’s periodic shift (65-year period) from predominately warm to predominately cool regimes, controls much of the climatic variability in the Northern Hemisphere. During warm (positive) AMO phases, the Northern Hemisphere is generally warmer, by as much as a few degrees Fahrenheit when compared to the cool phases. This cycle appears to be linked to periodic fluctuations in the strength of the thermohaline circulation (THC), or the “conveyor belt” that moves heat and salt around the world’s oceans. In the North Atlantic, a surface current transports warm water north and then “overturns” near Greenland and becomes a deep cold water current that moves south. The northward movement of warm water is strongest at about 30 degrees North (about the same latitude as New Orleans), where over 40 billion gallons of water pass each second! The strengthening of this current, which has been happening since the 1970’s, has corresponded to the rise in North Atlantic sea surface temperatures and Northern Hemisphere land temperatures.

Seasons: Winter, Spring, Summer, Fall

Sources: Knight, JR et al. “A signature of persistent natural thermohaline circulation cycles in observed climate.” Geophysical Research Letters 32 (2005): L20708 and Bryden, et al. “Slowing of the Atlantic meridional overturning circulation at 25 degrees N.” Nature 438 (2005): 655-657.

Climate Fact: Diatoms and Dinoflagellates

administrator — Wed, 08 Oct 2008 20:44:46 +0000

During the warm seasons (spring through fall), the water in the Baltic Sea is stable and stratified. This means that the warmest and least dense water is on the surface, and as you dive deeper and deeper, layers of progressively colder, saltier, and denser water are encountered. During the decades of the 1970’s and 1980’s, the North Atlantic Oscillation (NAO) was in a negative phase, and winters in the Baltic Sea were generally cold and dry. As a result, during the winter, the water on the surface would cool to the point where it was colder than the water below it, and mixing between the layers would occur until a new stable state (one where the cold water is on the surface) was reached. This annual mixing was important for the survival of the sea’s diatoms, which depended on the mixing that would take place during the spring as the sea reverted from the winter to summer water column formation. Diatoms are photosynthetic, single-celled organisms, which form a large part of the marine food pyramid’s base. A positive state of the NAO since the late 1980’s has corresponded to milder winters, and the deep mixing that would occur as the seasons changed no longer occurs. As a result, the diatoms that depend on the mixing have been largely replaced by another type of single-celled organism known as dinoflagellates, which may be best known for their whip-like tails that propel them through the water. This change has also corresponded to other changes in the sea’s species’ composition.

Seasons: Winter, Spring, Summer, Fall

Sources: Alheit, J. et al. “Synchronous ecological regime shifts in the central Baltic and the North Sea in the late 1980’s.” ICES Journal of Marine Science 62 (2005): 1205-1215 and Hinrichsen, HH et al. “Correlation analyses of Baltic Sea winter water mass formation and its impact on secondary and tertiary production.” Oceanologia 49 (2007): 381-395.

Climate Fact: Ice Break-Up Dates and Bears

administrator — Wed, 08 Oct 2008 20:36:11 +0000

Polar bears, Earth’s largest land predator, are most common on annual sea ice that sits over shallow seas. This ice provides the bears with a platform from which they can hunt for food. In Canada’s Western Hudson Bay region, which is at the southernmost extent of the polar bear’s range, winter and spring are the best times to hunt, as that is when there is the most ice cover and spring is when the most seals are available. By the time late spring and summer arrive, the Hudson Bay is ice-free, and the bears are essentially stranded from their prey until the ice freezes-up again. The bears must live on their fat reserves during this period, which generally lasts about four months. The earlier the ice breaks up in the spring, the less time the bears have to build fat reserves to survive the hungry periods. Warmer temperatures in the region mean that the ice is now breaking up an average of three weeks earlier than it did 30 years ago, and a correlation exists between the date of the break-up and starvation induced mortality in young and older bears. Overall, the region’s Polar Bear population declined from 1194 in 1987 to 935 in 2004. While healthy adult bears can usually survive the extra stress of earlier ice break-up, years when ice breaks-up especially early generally correspond to more human-bear encounters, as the bears stray from their usual territories to find food.

Seasons: Spring, Summer

Source: Regehr, EV et al. “Effects of Earlier Sea Ice Breakup on Survival and Population Size of Polar Bears in Western Hudson Bay.” The Journal of Wildlife Management 71 (2007): 2673-2683.

Climate Fact: Seabird Shift

administrator — Wed, 08 Oct 2008 20:00:36 +0000

Climate variability in the mid- to high-latitudes of the Northern Hemisphere, or the area from about 35 degrees North to the poles, is largely controlled by two naturally occurring climate oscillations, the Pacific Decadal Oscillation (PDO) and the North Atlantic Oscillation (NAO). In 1977, both oscillations shifted from negative to positive phases, which resulted in a warming of the ocean waters in the northeastern Pacific around Alaska, and a cooling of the waters in the northeastern Atlantic around Scandinavia. This shift in sea surface temperatures (SSTs) was one of the largest ever recorded. In 1989, the opposite trend happened. The magnitude of this shift, however, was much less pronounced. The population trends of two species of seabird, the Common Murre and the Thick-billed Murre, were studied in relation to these shifts. These species thrive under essentially the opposite environmental conditions. The large magnitude shift in 1977 caused populations of both species to decline throughout the entire hemisphere, while both populations grew after the smaller shift in 1989. Because these shifts produced opposite trends in local environmental conditions, it might be expected that one species would thrive and one species would decline in number during each of the regime shifts. Since this was not the case, this phenomenon illustrates how it can be difficult for top predatory species to adapt to any rapid climatic fluctuation.

Seasons: Spring, Summer, Fall

Source: Irons, D.B. et al. “Fluctuations in circumpolar seabird populations linked to climate oscillations.” Global Change Biology 14 (2008): 1455-1463.

Cliamte Fact: Seagrass and SSTs

administrator — Wed, 08 Oct 2008 18:43:28 +0000

The summer of 2003 was one of Europe’s warmest on record and maximum sea surface temperatures (SSTs) in the Mediterranean were well above average (by about 2.5 degrees Fahrenheit). These temperatures were the highest recorded between 1972 and 2004. Also during this period, years when the maximum water temperature was above average were years when there were above average numbers of seagrass plants flowering (these plants generally produce flowers only once every five years). In 2003, the Sea’s dominate seagrass species (Posidonia oceanica) flowered at record levels. While this phenomenon may suggest that warmer SST’s are good for seagrass, the overall warming trend in the Mediterranean of 1.7 degrees Fahrenheit since the early 1980’s has corresponded to an increase in seagrass mortality, a decline in the species’ areal extent, and a decline in rhizome growth (stalk-like plant structures that grow horizontally, usually underground) . Indeed, years of extensive flowering are often followed immediately by years of extensive mortality.

Season: Summer

Source: Diaz-Almela, E et al. “Consequences of Mediterranean warming events in seagrass (Posidonia oceanica) flowering records.” Global Change Biology 13 (2007): 224-235.

Climate Fact: Maritime Influences on Mountain Hemlock

administrator — Wed, 08 Oct 2008 18:25:55 +0000

In the Pacific Northwest, Mountain Hemlocks grow at elevations between 3,600 and 7,500 feet. These shade tolerant trees grow underneath the faster growing but shorter-lived Douglas Firs, and gradually make their way to the top of the canopy over their 700 year life spans. At the region’s high elevations, some of the world’s most extensive seasonal snowpack forms. The extent of this snowpack and its seasonal duration determine how much Mountain Hemlocks can grow each year. Warmer years (years when more precipitation falls as rain instead of snow, and the accumulated snow pack melts earlier in the spring) tend to be years of enhanced tree growth in the northern portion of the Hemlock’s range, and wider tree rings correspond to those years. In the southern extent of the Hemlock’s range (southern Oregon), however, the climate is different and warm temperatures and lack of snowpack limit hemlock growth. Here, the growth trends are essentially the opposite seen in the more northern areas of the species’ range. The Pacific Decadal Oscillation (PDO), a 50-year cycle of sea-surface temperature shifts in the northern Pacific, seems to largely control the depth and duration of Pacific Northwest snowpack. Positive (warm) phases of the PDO, which occurred between about 1920 until about 1945, and from about 1977 until just a few years ago, correspond to warmer temperatures in the Pacific Northwest and less snowpack.

Seasons: Winter, Spring, Summer, Fall

Source: Peterson, DW and Peterson, DL. “Mountain Hemlock Growth Responds to Climatic Variability at Annual and Decadal Time Scales.” Ecology 82 (2001): 3330-3345.

Climate Fact: El Niño and Tropical Pacific Cyclones

administrator — Wed, 08 Oct 2008 17:45:29 +0000

The tropical Pacific basin is one of the planet’s warmest ocean regions, with surface water temperatures rarely falling below 83 degrees Fahrenheit. These perennially warm temperatures provide the fuel for tropical cyclone formation, and the strongest cyclones on record have formed here. Because these waters are already above the threshold for tropical cyclone formation, slight increases in water temperature do not seem to have much of an effect on the average annual number and average intensity of cyclones forming here. Instead, the El Niño Southern Oscillation cycle appears to control how many cyclones form annually. In El Niño years, the region’s monsoon trough (a region of low pressure associated with the monsoon) extends farther east over the tropical waters than it does during La Niña years. This leads to a larger area where tropical cyclone formation is likely, and on average three times as many tropical cyclones form during El Niño than during La Niña years.

Seasons: Spring, Summer, Fall

Sources: Matsuura, T et al. “A mechanism for interdecadal variability of tropical cyclone activity over the western North Pacific.” Climate Dynamics 21 (2003): 105-117 and Chan, JCL. “Interannual variations of intense typhoon activity.” Tellus 59A (2007): 455-460.

Climate Fact: Tropical CAPE

administrator — Wed, 08 Oct 2008 17:42:41 +0000

Convective available potential energy (CAPE) is a measure of how much energy is available for storm development (CAPE is measured by the number of joules present in a kilogram of air). Generally, the hotter and more humid conditions are, the more CAPE is present. A collection of atmospheric conditions, including some CAPE, are necessary for a storm to develop. Thus, while CAPE does not tell you whether there will be a storm or not, it does tell you how severe a storm that does develop is likely to be. Since the late 1950’s, the average amount of CAPE in the tropics has been growing at a rate of 86 joules per kilogram per decade, or six percent per decade. This trend has been the most pronounced in the western tropical Pacific.

Seasons: Winter, Spring, Summer, Fall

Source: Gettelman, A. “Multidecadal trends in tropical convective available potential energy.” Journal of Geophysical Research 107 (2002): ACL 17.

Climate Fact: Rainfall Reductions and Indian Ocean Warming

administrator — Wed, 08 Oct 2008 17:32:40 +0000

Eighty-three (83) percent of the moisture entering tropical Africa originates in the Indian Ocean. Over the last four decades of the 20th century, sea surface temperatures (SSTs) in the tropical Indian Ocean rose by nearly two degrees Fahrenheit, making these waters the warmest they have been in 120,000 years. As this has happened, rainfall over the Indian Ocean has increased by about 20 percent. This increase means that more heat is being released into the upper atmosphere over the ocean, and as this has happened, the circulation system that brings moisture from the ocean to the African continent has moved and onshore winds have weakened. This process has been linked to a 15 percent decline in growing season rainfall that occurred in East Africa over the same period that Indian Ocean SSTs rose.

Seasons: Winter, Spring, Summer, Fall

Source: Funk, C et al. “Warming of the Indian Ocean threatens eastern and southern African food security but could be mitigated by agricultural development.” Proceedings of the National Academy of Sciences 105 (2008): 11081-11086.

Climate Fact: Copepod Range Change

administrator — Wed, 08 Oct 2008 17:28:24 +0000

The Labrador Sea Water (LWS) is a stream of cold, fresh, and oxygen rich water that travels down the western Atlantic coast from the Labrador Sea, which is located between Greenland and Newfoundland, towards the Equator. This stream forms in the late fall/early winter after the seasonal accumulation of glacial melt water, which is less dense than salt water, has pooled on the surface. As the strong northwesterly winter winds start to blow across the Labrador Sea, the fresh water pool cools, sinks to a depth of about 5,000 feet, and travels down the East Coast of Canada. The North Atlantic Oscillation (NAO), or the cyclical change in the pressure difference between the Azores High and Icelandic Low, controls the strength of these winds. During positive NAO phases (when the Azores High is particularly high and the Icelandic Low is particularly low), the winds are stronger, which leads to more cooling on the surface and a stronger flow of the Labrador Sea Water. The stronger the flow of this water, the cooler the waters along America’s east coast are. Over the last 30 years, the NAO was strongly and predominately positive, and copepod species (small crustaceans that collectively constitute the biggest source of protein in the oceans) that were previously found only in the waters off Canada, began showing up as far south as New Jersey, and increased in abundance all along the New England coast.

Seasons: Fall, Winter

Source: Johns, DG. “Arctic boreal plankton species in the Northwest Atlantic.” Canadian Journal of Fisheries and Aquatic Sciences 58 (2001): 2121-2124.

Climate Fact: Warming and Water Discharge

administrator — Wed, 08 Oct 2008 17:23:02 +0000

The Arctic Ocean is surrounded by a series of river drainage basins, which collectively occupy an area 1.5 times that of the ocean basin itself. No other ocean basin’s temperature and salinity levels are more dependent on what happens on the adjacent land surface. These temperature and salinity levels in turn influence the behavior of the world’s ocean conveyor system, which transports heat and nutrients to and from different ocean basins. The Eurasian Arctic has warmed by about 1.3 degrees Fahrenheit since the 1930’s. As this has happened, the total combined annual discharge of the six largest Eurasian rivers that flow into the Arctic Ocean has grown by 34 trillion gallons, or seven percent. These trends have corresponded to increases in winter precipitation and thawing permafrost. Total discharge also appears to be related to the behavior of the North Atlantic Oscillation (NAO), or the cyclical change in the pressure difference between the Azores High and Icelandic Low. Positive phases bring more precipitation to Scandinavia and Siberia, and the NAO has been predominately and strongly positive over the last 30 years.

One of the six rivers studied is Russia’s Lena River. To see a colorful LANDSAT image of the Lena River Delta, visit http://earthasart.gsfc.nasa.gov/lena.html.

Seasons: Spring, Summer, Fall

Sources: Peterson, BJ et al. “Increasing River Discharge to the Arctic Ocean.” Science 298 (2002): 2171-2173 and Serreze, MC et al. “Large-scale hydro-climatology of the terrestrial Arctic drainage system.” Journal of Geophysical Research 108 (2003): doi:10.1029/2001JD000919 and McGuire, AD et al. “Land cover disturbance and feedbacks to the climate system in Canada and Alaska.” Chapter 9 (pages 139 - 161) in Imzd Change Science: Ohsel-virzg, Moniloritig, and Ulzder*stnditzg Trojectol-ies of Challge OH the Earth’s SU+KZE. ditcd by Gutman, C., Janetos, A.C., Justice, C.0, Moran, E.F., Mustard, J.F., Rindf~lssR, .R., Skole, D., Turner 11, B.L., and Cochrane, M.A. Dordrecht, Ncthcrlands, Kluwer Adademic Publishers.

Climate Fact: North Sea Species Richness

administrator — Wed, 08 Oct 2008 17:06:46 +0000

While land and sea surface temperature trends are the most common measures of climate change, changes in bottom temperatures, especially in shallow seas, can have major implications for marine species. Ocean species can generally adjust their ranges more easily than land species, as there are fewer geographic barriers in the ocean and many fish species use the free energy ocean currents provide to disperse their larvae. In the North Sea, which sits between Great Britain and Scandinavia, the average wintertime bottom temperature has increased by almost four degrees Fahrenheit since the early 1970’s, a rate that is more than ten times faster than the global average. As this has happened, species that formerly could only survive in the warmer waters to the south moved into the North Sea, and species that are accustomed to the cooler temperature regimes now seen in more northerly waters shifted their ranges north. Overall, during the last 30 years, more species moved into the North Sea than moved out, and the number of fish species living in the North Sea is now 50 percent higher than it was in the early 1970’s.

Seasons: Winter, Spring, Summer, Fall

Source: Hiddink, JG and Hofstede R Ter. “Climate induced increases in species richness of marine fishes.” Global Change Biology 14 (2008): 453-460.

Climate Fact: ENSO and Tropical Cyclone Landfall Frequency

administrator — Wed, 08 Oct 2008 16:45:58 +0000

The El Niño Southern Oscillation (ENSO) cycle, or the cyclical movement of heat in the tropical Pacific Ocean, affects the upper atmosphere over the Atlantic Ocean. This affects both the frequency of Atlantic tropical cyclone formation as well as the positioning of the region’s high and low pressure centers that steer the tropical cyclones. La Niña conditions are 19 percent more common during years when tropical cyclones frequently make landfall along the Atlantic and Gulf Coasts of the United States. El Niño conditions are 10 percent more common during years when few tropical cyclones make landfall along the U.S. coast.

Seasons: Spring, Summer, Fall

Source: Lyons, Steven. “U.S. Tropical Cyclone Landfall Variability: 1950-2002.” Weather and Forecasting 19 (2004): 473-480.

Climate Fact: North Atlantic Basin Warming

administrator — Tue, 07 Oct 2008 20:38:39 +0000

The amount of energy that the North Atlantic Basin accumulated over the last 50 years is equivalent to almost four trillion tons of TNT (1.610 × 1022 joules). This energy has not been distributed uniformly, as the tropical and subtropical regions of the North Atlantic have warmed the most, and the subpolar region has actually cooled. More energy has been gained than lost, however, and if this gain was averaged out across the entire North Atlantic Basin, each square meter would have experienced an increased heat flux of 0.42 Watts. This heat gain and change in heat distribution is related to the behavior of the North Atlantic Oscillation (or the cyclical change in the pressure difference between the Azores High and Icelandic Low), which transitioned from a predominately negative phase during the 1950’s and 1960’s to a predominately positive phase during the 1980’s and 1990’s. While multi-decadal heat fluxes from one ocean basin to another have been part of Earth’s climate for centuries, each of the world’s ocean basins have warmed over the last 50 years and the average temperature of the upper 3000 meters (which is about 70 percent of the world’s ocean water) rose by 0.07 degrees Fahrenheit. While this number may seem small, the same amount of energy it would take to raise the world’s ocean heat content by just 0.18 degrees would be enough to raise the average global atmospheric temperature to the boiling point of water, or 212 degrees!

Seasons: Winter, Spring, Summer, Fall

Source: Lozier, MS, et al. “The Spatial Pattern and Mechanisms of Heat-Content Change in the North Atlantic.” Science 319 (2008): 800-803 and Sources: Levitus, S. et al. “Warming of the world ocean, 1955-2003.” Geophysical Research Letters 32 (2005): L02604, doi: 10.1029/2004GL01592 and Miles, Edward. “Multiple Stresses, Thresholds, and Ocean Acidification.” Cannon House Office Building, Washington, DC. 20 September 2007

Climate Fact: ENSO and Gulf Coast Lightning

administrator — Tue, 07 Oct 2008 20:27:42 +0000

The El Niño-Southern Oscillation (ENSO), or the cyclical movement of heat in the tropical Pacific Ocean, affects atmospheric phenomena throughout the world. The cycle affects the strength and position of the Pacific Jet Stream, an upper atmosphere wind current that flows from the Pacific over North America. During La Niña phases of the cycle, the Jet Stream is weaker than average and flows in an arcing pattern over the northern U.S. During El Niño phases, the Jet Stream strengthens and flows over the southern United States. In general, this leads to a stormier Gulf Coast, and a 100-200 percent regional increase in the frequency of warm season lightning strikes compared to neutral conditions.

Seasons: Spring, Summer, Fall

Sources: Cook, AR and Schaefer, JT et al. “The Relation of the El Niño-Southern Oscillation (ENSO) to Winter Tornado Outbreaks.” Monthly Weather Review 136 (2008): 3121-3137 and LaJoie, M and Laing, Arlene. “The Influence of the El Niño-Southern Oscillation on Cloud-to-Ground Lightning Activity along the Gulf Coast. Part I: Lightning Climatology.” Monthly Weather Review 136 (2008): 2523-2542.

Climate Fact: Sea Level Rise on the East Coast

administrator — Tue, 07 Oct 2008 20:13:09 +0000

Over the past century, measurements taken at geologically stable locations show that the global sea level rose by eight inches, with most of this rise happening over the second half of the 20th century. Measurements taken at most coastal locations, however, rarely correspond to this global value because near-shore environments are naturally dynamic. Storms, natural sedimentation, water course alterations, and land subsidence (often due to groundwater withdrawals) can all work to either raise or lower a locality’s relative sea level. There are also significant annual and multiannual variations in local sea levels, which on the East Coast of the United States appear to come in one- to three-year cycles (depending on the location), with a difference of about eight inches from peak to peak. These fluctuations appear to be linked to the behavior of the North Atlantic Oscillation, or the periodic change in the difference in atmospheric pressure between a low pressure center around Iceland and a high pressure center around the Azores Islands, located about 900 miles west of Portugal. Changes in the Icelandic Low have been linked to changes in the behavior of the North Wall of the Gulf Stream, or the stream of water that runs off the U.S. East Coast towards the middle of the Atlantic. Fluctuations in the strength and position of the North Wall appear to be largely responsible for causing the changes in the waves and winds that determine sea levels along the East Coast.

Seasons: Winter, Spring, Summer, Fall

Sources: Hong, BG et al. “Sea Level on the U.S. East Coast: Decadal Variability Caused by Open Ocean Wind-Curl Forcing.” Journal of Physical Oceanography 30 (2000): 2088-2098 and Kolker AS and Hameed, S. “Meteorologically driven trends in sea-level rise.” Geophysical Research Letters 34 (2007): L23616 and Hameed, S and Piontkovski, S. “The dominant influence of the Icelandic Low on the position of the Gulf Stream.” Geophysical Research Letters 31 (2004): L09303.

Climate Fact: Cotton Yields and Climate

administrator — Tue, 07 Oct 2008 20:09:02 +0000

A common cotton disease in the southeast, hardlock, is caused by fungus and affected by temperature and humidity. The disease does better during years when humidity and rainfall levels are above average, especially during the months of July to September, when cotton plant flowers and bolls (pods containing 32 seeds from which the cotton fibers grow) mature. During the wet and humid year of 2002 in Florida, hardlock caused crop yields to decrease from 650 pounds per acre to 400, or 20 million dollars in lost yield. Drier and less humid years, on the other hand, discourage fungal growth and favor high yields. Over 50 percent of the variability in yields in the southeastern U.S. can be explained by climate. Years with the highest cotton yields correspond to years with lower than normal sea surface temperatures (SSTs) in the Gulf of Mexico and Atlantic Ocean, where the winds that blow into the southeast during the summer originate. These lower SSTs mean less humidity, and cause relatively dense air to become concentrated in upper air masses, which discourages convective cloud formation and rainfall.

Seasons: Summer, Fall

Sources: Baigorria, GA et al. “Assessing Predictability of Cotton Yields in the Southeastern United States Based on Regional Atmospheric Circulation and Surface Temperatures.” Journal of Applied Meteorology and Climatology 47 (2008): 76-90 and The University of Florida Education and Research Center. “Cotton/Hardlock.” Accessed Online 1 October 2008 <http://nfrec.ifas.ufl.edu/cottonhardlock.htm> and Cotton’s Journey. “The Story of Cotton.” Accessed Online 1 October 2008 <http://www.cottonsjourney.com/storyofcotton/page3.asp>

Climate Fact: North Atlantic Seabird Success

administrator — Tue, 07 Oct 2008 19:51:53 +0000

Seabirds, such as auks, gulls, petrels, terns, and gannets, have spent tens of millions of years adapting to life on the ocean. Some species, such as the Sooty Tern, can spend years at sea before returning to land. The success of these species is dependent on the success of their food sources (such as fish and plankton), and the success of these food sources is dependent on oceanic conditions such as sea-surface temperatures and the behavior of ocean currents. In the North Atlantic, changes in the North Atlantic Oscillation (NAO), or the cyclical change in the pressure difference between the Azores High and Icelandic Low, affect ocean currents. A 30-year study of summertime seabird breeding success indicates that seabird species on both sides of the Atlantic have more offspring in years when the waters are warmer, and in years when the previous year’s winter featured a predominately negative NAO (a negative NOA means that the difference between the aforementioned pressure centers is lower and the westerly winds blowing across the ocean are not as strong). The North Atlantic Basin has experienced an overall warming trend over the last 50 years, although the sub-polar waters, where most of the breeding activity takes place, have actually cooled. Also during this period, the NAO has transitioned from being predominately negative to predominately positive.

Seasons: Winter, Spring, Summer, Fall

Source: Sandvik, H et al. “A latitudinal gradient in climate effects on seabird demography: results from interspecific analyses.” Global Change Biology 14 (2008): 703-713.

Climate Fact: Nematode Response to Water Temperature

administrator — Tue, 07 Oct 2008 19:39:20 +0000

Ranging in size from barely visible to nearly 30 feet long, nematodes, or roundworms, are the most abundant animals on Earth. Because they comprise a substantial percentage of the animal life on the seafloor, changes in their abundance and diversity there can have major implications for ocean ecosystems. Between 1992 and 1994 in the deep waters of the Cretan Sea in the eastern Mediterranean, an ocean current anomaly caused a 0.72 degree Fahrenheit plummet of bottom water temperatures. As this happened, there was a doubling of the total number of nematode species living on the bottom of the Cretan Sea, which was largely due to Atlantic nematode species coming into the Mediterranean from the north. The absolute nematode abundance, however, dropped by as much as 65 percent. As the waters began to warm after 1994, nematode abundance began to recover, but the number of nematode species began to decline.

Seasons: Winter, Spring, Summer, Fall

Source: Danovaro, R et al. “Biodiversity response to climate change in a warm deep sea.” Ecology Letters 7 (2004): 821-828.

Climate Fact: Strengthening Upwelling Patterns

administrator — Tue, 15 Apr 2008 20:10:22 +0000

Ocean currents transport heat from the Equator to the higher latitudes, as well as nutrient rich water from the depths of the ocean to the surface. The transport of cooler, nutrient rich water upward is a process known as upwelling. Upwelling feeds much of the life at the ocean’s surface, and 20 percent of the World’s fish catch occurs in areas where the upwelling is strong, although these areas account for only about one percent of the Planet’s ocean surface area. The Canaries Current, a southward moving current that brings cold, nutrient rich water up to the Moroccan Coastline, feeds a valuable fishery there. In the past century, the Sahara Desert Region has warmed faster than the adjacent ocean waters. This means that the low pressure zone over the Sahara desert has become lower and the high pressure zone that sits over the ocean has not changed that much, which has increased the pressure difference between these zones. Because the difference in pressure between the land and the ocean drives the winds that “pull” cold waters from the depths of the ocean to the surface, the winds have strengthened, and the upwelling has also strengthened. Over the Twentieth Century, the surface waters off the Moroccan coast have cooled by about 2.2 degrees Fahrenheit. Although other warm periods over the past 2,500 years have also corresponded to a strengthening of this current, the cooling that has happened over the past century is unprecedented.

Seasons: Winter, Spring, Summer, Fall

Source: McGregor, H.V. et at. “Rapid 20th-Century Increase in Coastal Upwelling off Northwest Africa.” Science 315 (2007) 637-639.