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