1 / 30

Abyssal Plains

Abyssal Plains . Tim Lamothe, Julie van der Hoop & Sara Wanono. Lecture Outline. Physical and chemical characteristics of the abyssal plains Characteristics of abyssal fauna and an overview of deep-sea food supply Research & sampling methods Response of the benthos Whale Fall Ecology

ryanadan
Download Presentation

Abyssal Plains

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Abyssal Plains Tim Lamothe, Julie van der Hoop & Sara Wanono

  2. Lecture Outline • Physical and chemical characteristics of the abyssal plains • Characteristics of abyssal fauna and an overview of deep-sea food supply • Research & sampling methods • Response of the benthos • Whale Fall Ecology • Limitations of deep sea science

  3. Characteristics of the Abyss • The abyssal zone (2000-6000m deep) is the single largest habitat on Earth, covering 300,000,000 km2 • The abyssal plains, located in the aphotic zone at depths of 4000-6000m, are the flattest of all the Earth’s topographical regions. • 40% of total seafloor and ¼ of earth’s surface • Average slope of less than 1 meter per horizontal kilometer

  4. Abyssal Sediment • Broad, relatively featureless expanses of mainly land-derived sediment, usually carried by turbidity and riverine currents. • Underlying topography is blanketed by massive amounts of sediment • Range of thickness: 100 meters – more than 1 kilometer • The principal sediment constituents on abyssal plains are brown clays and the siliceous remains of radiolarian zooplankton and such phytoplankton as diatoms.

  5. Properties of Abyssal Plains • Water temperature in the abyssal zone ranges from 0 to 4 degrees Celsius. • Abyssal salinities range narrowly around 35 parts per thousand. • The abyssal zone is characterized by immense pressure, generally ranging between 200 and 600 atmospheres.

  6. Properties of Abyssal Plains • Deep sea waters of the abyssal plains are aerated by the advection of cold, dense, oxygen rich polar water. • The nutrient salt concentration is higher in abyssal waters than in overlying waters because the abyssal zone acts as a reservoir for the salts from decomposed biological materials

  7. Light in the Deep Sea Complete lack of sunlight precludes any photo-synthetically derived primary productivity This, then, begs the question, from which so much of thescientific study of the deep sea is born – how can organismsfeed, or even live, in the deep sea?

  8. Benthic dwellers • Epifauna • Infauna • Nektobenthos • Community structure less stable • Limiting factor

  9. Adaptations to obtain prey • Photosynthetic production cannot occur • Sensory devices • Long antenna • Detect motion • Sharp teeth • Hinged jaws • Expandable bodies • Bioluminesce

  10. Food sources • Season phytoplankton bloom • Fecal pellets • Crustacean molts • Fish dumping

  11. Food sources • Dead fish and mammals • Floating algae • Detritus • Biogenious sediments • 1-3% of surface organic primary production reaches the abyssal seabed

  12. Ecological Trends • Whole animal food falls occur on a smaller scale • Coastal macroalgae and seagrass have often been encountered in sediment traps • Deep sea epifaunal deposit feeders ingest macroalgae and seagrass

  13. Ecological Trends • Food falls provide energy and its presence influences the structure of benthic communities • Organic primary production is converted to bacterial tissue

  14. Ecological Trends • Evidence of strong correlation between phytodetrital material found in the deep-sea and surface water productivity. • Nutritive values are reduced because of the long residence times in the water column.

  15. Ecological Trends • Phytodetritus deposits are likely a major influencing factor affecting large blooms of phytoplankton in surface waters • Variation in the timing and amount of this deposition from year to year. • Seasonal drops of phytodetritus are considered a major source of energy for the deep-sea community

  16. Methods • Photography • Visual evidence • Transects

  17. Methods • Cores: Small, but quantitative measurements • Box Cores: Effects of bow wave • Tube Cores: Preserve conditions at sediment-water interface Gage and Bett 2005

  18. Methods • The MEGACORER • 12 10cm diameter cores • Penetrate 20-40cm into sediment • Sample size: 942.5cm2 Gage and Bett 2005

  19. Methods • Phytopigments: • Determination of phytodetrital makeup, source, age, depth penetration. • Chlorophyll a: intact phytoplankton cells, indicates undegraded material. • Phaeopigments: degradation product of chlorophyll, indicates breakdown. • Chlorophyll a:Phaeophorbide ratio (R): small for relatively undegraded material. Thiel et al. 1988: R=1.64 and 2.04 compared to value of 42.1 in a Holothurian stomach. Thiel et al. 1988

  20. Methods • Phytopigments • Chlorophyll b: terrestrial input • Fucoxanthin and other carotenoids: diatoms and dinoflagellates. • Inorganic Composition • Rarely reported • Percentage of CaCO3 can infer relative abundance of coccolithophorids • 2% at Sta M (NE Pacific) • 62% at PAP (NE Atlantic)

  21. Methods • Sediment Community Oxygen Consumption (SCOC) • Measure of the rate of organic matter mineralization by sediment community. Does not differentiate between taxonomic groups. • Increase in SCOC following organic matter sedimentation indicates increased respiration • Indicates a benthic response

  22. Benthic Response: SCOC • Drazen et al. 1998 (NE Pacific, Sta. M): maxima coincide with periods of peak POC flux. Significant increase in SCOC from Feb to June. No significant difference between years. • Smith et al. 2001 (NE Pacific, Sta. M): seasonal fluctuation in relative synchrony with POC flux. Over 8 years, remarkably consistent. Drazen et al. 1998

  23. Benthic Response • Bacteria colonize & transform detritus • Benthic meiofauna quickly colonize: response is < 3 h. • Affects species composition, distribution, abundances on short term: rapid aggregation and dispersal of specialists.

  24. Thurston et al. 1994 • Three N. Atlantic sites separated by 40°N, at similar depths (4850-5440m). • Latitude marks separate physical mixing characters; distinct fish communities, benthic groups. • PAP: North of 40°N, dominated by “vacuum cleaning” holothurians. Detritivores high. • GME and MAP: South of 40°N, dominated by asteroids and decapods. Carnivores high. • PAP site receives larger total POC flux, in aggregated forms, on seasonal cycles, than southern sites. • Shows that megafaunal organism type and size can be different at the same depth: food abundance and delivery is of great importance to faunal community.

  25. Depth Profile of Response • Drazen et al. 1988 • Chlorophyll a levels decrease with sediment depth. • ATP (measure of respiration of sediment community) also decreases with depth • Surface organisms gain a greater benefit from inputs of phytodetritus than deep-sediment dwelling organisms.

  26. Whale Falls An oasis in the abyssal desert • The periodic falls of large whale carcasses provide massive pulses of labile organic matter to the deep sea • Species richness at whale falls rivals that at hydrothermal vents • Characterized by four distinct, successional stages:1) mobile scavenger stage2) enrichment opportunist stage3) sulphophilic stage4) reef stage • Evidence suggests whale falls act as deep sea stepping stones for various taxa as they make their way across the seafloor to hydrothermal vents and cold seeps.

  27. Limitations • Relatively inaccessible • scientists must often rely on “snapshots” (short sampling periods) • Greater difficulty of replicated sampling within a relatively small area of seabed when using a surface vessel in deep water. • Technology is expensive • Bringing deep sea sediment to the surface can result in decompression of sediment and disruption of initial composition. • Transporting fauna to surface can interfere with integrity of samples • Delicate process: sampling methods can disrupt original state of biogenic structures, sediments, etc. • Extensive study of certain areas, but none of others – are findings truly representative of global deep sea trends?

  28. Questions?

More Related