Oceanic Zone Oceanic Zone – The ocean NOT over the
continental shelves.Stratified over the abyssal plain @ approximately 6000m.
LAYERS (Relationship to Surface) Photic Zone = Epipelagic – to 200m “Twilight” Zone = Mesopelagic – 200m-1000m
Deep Lightless Zones = Bathypelagic (1000m-2000m) & Abyssopelagic (>2000m); 4ºC and less
Oceans
Surface & Intermediate Waters Most of the Oceanic Zone has a permanent
thermocline between 500-800m (Mesopelagic). Above this = affected by wave action and considered the surface waters.Temporary thermocline may form @ approximately 30-50m in the temperate zone in summer.
Under 800m but well above the Abyssal Plain = intermediate waters (many water masses and, potentially, thermoclines & haloclines)
Bottom Waters Waters slowly flowing above the Abyssal
Plain = bottom waters. Antarctic Bottom Water (AABW) is slowly
flowing over the bottom in most of the ocean.
North Atlantic Deep Water (NADW) is slowly flowing over the bottom in the northern part of the North Atlantic.
These water masses are usually very well oxygenated.
Oceanic Upwelling and Downwelling Upwelling due to:
-diverging currents (from air circulation)-deep currents encountering physical barrier-“deep current” upwelling
Ocean “Conveyor Belt”
Primary Production
Abyssal Plain Sediments
Ocean Floor
Epipelagic To 200 m If nutrients sufficient then much phytoplankton
& zooplankton. Epipelagic fishes usually streamlined and
counter shaded or reflective (constant swimming). Other organisms often transparent.
Epipelagic Food Web
grazing zooplankton
predatory zooplankton
bacteria
phytoplanktonphytobacteria
dissolved organiccompounds (DOC)
“predatory” fishes, mollusks, etc.
phyto-plankti-vorousfishes
microzooplankton
larger “predatory” fishes, mammals, etc.
Mesopelagic 200-1000m; “Twilight Zone” Effectively no primary productivity Most mesopelagic organisms rise into the
epipelagic to feed at night. Fishes black or silvery, others transparent. Photophores = light generating “organs” Lanternfishes = most common fishes.
MesopelagicDeep Scattering Layer.
Mesopelagic fishes & other animals migrate toward the surface at night to feed.This mobile deepwater community is dense enough that it reflects sonar.
Mesopelagic fishes usually have swimbladders.
Deep Scattering Layer - Day
Deep Scattering Layer
Deep Scattering Layer - Night
Deep Scattering Layer
Bathy- & Abyssopelagic approx. 1000-6000m; no light, no primary
productivity, cold Fishes and most other animals are
sedentary and wait for food to arrive from above (usually big mouths and long teeth)
Fishes and crustaceans are black or bright red and may have a few photophores.
No swimbladders & “flabby”
Bathy- & Abyssopelagic Food Web
predatory/scavenging animals(cnidarians, mollusks, crustaceans, fishes, etc.)
particulate organicmatter (POM)
collecting/scavenging animals(mollusks, crustaceans, fishes, etc.)
Bathy- & Abyssopelagic
Oceanic Benthic (Abyssal Plain) No light, no primary productivity, cold Fishes and other organisms usually black,
transparent, or silvery (few photophores). Usually less “flabby.” Many echinoderms.
Abyssal Benthic Food Web
predatory animals(echinoderms, mollusks, crustaceans, fishes, etc.)
bacteria
dissolved organiccompounds (DOC)
particulate organicmatter (POM)
collecting/scavenging animals(annelid worms, echinoderms, mollusks
crustaceans, fishes, etc.)
larger predatory animals(mollusks, crustaceans, fishes, etc.)
Oceanic Benthic
Hydrothermal (Hot) Vents Ocean floor primary production via bacteria.
6CO2 + 6H2O + 3H2S → C6H12O6 + 3H2SO4
Free living and symbiotic with annelids (Pacific) or bivalve mollusks (Atlantic).
Vents ephemeral (communities temporary).
Methane (Cold) Seeps Ocean floor primary production via bacteria
that use CH4 in chemoautotrophy. Many free living and others symbiotic (often
involving tube worms and/or bivalves). Methane seeps more constant.
Vertical Migration Most mesopelagic organisms migrate
vertically every day. Most/many larvae enter the epipelagic or
upper mesopelagic for early development. Some abyssal plain organism larvae only
enter the abyssopelagic until they find a place to settle.
El Niño/La Niña Pacific equatorial winds
(to west = “normal”/niña; to east = el niño).
El Niño/La Niña
Human Impacts Difficult to define or even address. Oceanic Zone enormous
Fishing activities significant in epipelagic), over fished in many places.Oceanic plastic trash of greater concern. Collects in centers of oceanic gyres. Microplastics.
Climate Change – carbon sink (?) and carbon saturation; ocean conveyor belt; climate regulation