Marine Ecosystems - Lecture Outline - Walker Smith I. Major issues facing oceanography and marine ecologists A. Controls on oceanic productivity: iron vs. grazing B. Role of the ocean in global carbon cycle C. Ecology and geochemistry of hydrothermal vent systems D. Upwelling systems and large-scale change II. Introduction: GLOBAL CHANGE A. Global warming 1. Many gases released by man's activities absorb infrared radiation [recall the chart of satellite sensor use and its limitation in the infrared region]; so as solar radiation enters the atmosphere, its absorption by molecules causes and increase in the thermal energy, and the temperature rises; as visible wavelengths are absorbed on the surface, some of the energy is re-emitted as IR, which then is absorbed in the atmosphere; therefore, the increase in IR absorbing gases must ultimately result in an increase in temperature; The questions are 1) when will it start?, and 2) what will its effects be? B. CO2 1. Carbon cycle [3]; discuss role of ocean and large reservoirs 2. oceanic cycle and biological pump [4] 3. increases in atmosphere; cyclic variations [5]; gradient from the southern to the northern hemisphere 4. model results C. Ocean as a CO2 source/sink D. Additional topics: global warming might intensify coastal upwelling; use of oxygen isotopes to validate carbon sinks (suggest ocean as sink of carbon of 2 gigatons); ice record of greenhouse gases (suggest that gases amplify orbital forcing of climate); snow-ice albedo uncertainty (results in a global mean climate about 1o warmer than original simulation, and an increase in precipitation of >7% worldwide); phytoplankton-S-albedo and climate (the DMS story) E. Role of ocean (Sarmiento and LeQuere, 1996); in the model without biology, solubility effects and the decrease in thermohaline circulation greatly decrease the removal of carbon dioxide by the ocean; the rate of thermohaline circulation reduction is controlled by the rate of CO2 build up; 1. Biological processes poorly known and constrain the accuracy of the estimates of oceanic uptake 2. Most of the CO2 uptake occurs in the southern ocean; it also is the region which that has the largest impact on oceanic CO2 uptake III. Role of iron in primary productivity and export production A. Based on trace metal clean sampling, we now realize that the concentrations of trace metals in the ocean are vanishingly small B. Using these techniques, John Martin showed that by small additions to waters in HNLC (describe) regions creates rapid growth of phytoplankton, and suggested that iron limitation was controlling CO2 sequestering in the ocean; C. mesoscale iron addition; Coale et al. 1. Chlorophyll increased from 0.2 to 3.0 ug/l by day 7 2. Iron decreased to <0.2 nM by day 9, and chl began to decrease thereafter 3. CO2 decreased from > 530 to less than 470 uatm 4. Nitrate dropped from >10 to less than 7 uM 5. Sequence of responses: physiological (chlorophyll production but no increase in carbon assimilation; increase in photosystem II rapid; increase in C assimilation lags ca. 24 h, followed by a biomass increase 6. Larger diatoms were the most increased (85x); picoplankton doubled, as did microzooplankton; mesozooplankton also increased two-fold, but clearly not enough to control diatoms; much of the export was in the form of diatoms, likely either via vertical mixing or aggregate formation 7. Iron naturally comes both from above (aeolian) as well as from below (via mixing and upwelling); in EqPac it is mostly from below via upwelling, and hence the rate of upwelling controls not only production but community structure and export 8. Hence, during periods of increased iron inputs (glacial maximum when dust transport is increased and sea level in minimal), production might be greater (controversial) 9. Also showed that ecosystem manipulations in the ocean are possible 10. Next step: Southern Ocean and polar front IV. Hydrothermal vents A. Vents were hypothesized a number of years ago based on our knowledge of the ocean's topography and genesis (plate techtonics) B. Discovery of "gutless worms" created a scientific storm, since it showed that ecosystems were capable of being driven by chemosynthetic mechanisms; further investigations showed systems being driven by methane seeps as well (Florida escarpment) C. Energy flow in vents V. General A. Def.: regions where physical processes cause a divergent flow, and which is replaced by cooler, nutrient-rich water from below; describe Ekman spiral and flow B. By physically displacing the surface water and replacing it with nutrient-rich water, upwelling creates an ideal means for optimal and continuous primary production; the large production is ultimately passed up the food web to form the world's richest marine systems D. Coriolis force is the force that creates the Ekman spiral; it is equal to 2 sin v, which indicates that it is greatest at the equator; acts perpendicular to the motion of the particle and to the right in the Northern hemisphere VI. Coastal upwelling systems A. Occurrence B. Atmospheric forcing 1. forcing for upwelling based on large scale atmospheric movements caused by differential heating and cooling of earth C. Energy transfer D. Interannual variability 1. by far more important variations occur from year to year; the major variation is called El Nino; def.: a large-scale disturbance in the production-consumption cycle of upwelling systems 2. Data on El Nino-Southern Oscillation events a. frequency b. Southern Oscillation Index: e. effects of El Nino not confined to sea; 1. climate of U.S. also affected during some El Nino's f. speed on onset of El Nino: g. winds during El Nino: remain the same or in fact increase j. Data for a kelvin wave VII. The 1982-3 ENSO VIII. The Present ENSO * * * * * * * * * * * * * * * * * * * * * * * * Walker O. Smith Department of Ecology and Evolutionary Biology Phone 423-974-5226 569 Dabney Hall Fax 423-974-3065 University of Tennessee, Knoxville, TN 37996