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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

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abyssal plains

Abyssal Plains

Tim Lamothe, Julie van der Hoop & Sara Wanono

lecture outline
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
characteristics of the abyss
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
abyssal sediment
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.
properties of abyssal plains
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.
properties of abyssal plains7
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
light in the deep sea
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?

benthic dwellers
Benthic dwellers
  • Epifauna
  • Infauna
  • Nektobenthos
  • Community structure less stable
  • Limiting factor
adaptations to obtain prey
Adaptations to obtain prey
  • Photosynthetic production cannot occur
  • Sensory devices
  • Long antenna
  • Detect motion
  • Sharp teeth
  • Hinged jaws
  • Expandable bodies
  • Bioluminesce
food sources
Food sources
  • Season phytoplankton bloom
  • Fecal pellets
  • Crustacean molts
  • Fish dumping
food sources12
Food sources
  • Dead fish and mammals
  • Floating algae
  • Detritus
  • Biogenious sediments
  • 1-3% of surface organic primary production reaches the abyssal seabed
ecological trends
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
ecological trends14
Ecological Trends
  • Food falls provide energy and its presence influences the structure of benthic communities
  • Organic primary production is converted to bacterial tissue
ecological trends15
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.
ecological trends16
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
methods
Methods
  • Photography
    • Visual evidence
    • Transects
methods18
Methods
  • Cores: Small, but quantitative measurements
    • Box Cores: Effects of bow wave
    • Tube Cores: Preserve conditions at sediment-water interface

Gage and Bett 2005

methods19
Methods
  • The MEGACORER
    • 12 10cm diameter cores
    • Penetrate 20-40cm into sediment
    • Sample size: 942.5cm2

Gage and Bett 2005

methods20
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

methods21
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)
methods22
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
benthic response scoc
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

benthic response
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.
thurston et al 1994
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.
depth profile of response
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.
whale falls
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.
limitations
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?
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