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
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
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 dissolved organic compounds (DOC) phytoplankton phytobacteria bacteria microzooplankton phyto- plankti- vorous fishes grazing zooplankton predatory zooplankton “predatory” fishes, mollusks, etc. 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.
Mesopelagic • Deep 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 particulate organic matter (POM) collecting/scavenging animals (mollusks, crustaceans, fishes, etc.) predatory/scavenging animals (cnidarians, mollusks, crustaceans, fishes, etc.)
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 bacteria particulate organic matter (POM) dissolved organic compounds (DOC) collecting/scavenging animals (annelid worms, echinoderms, mollusks crustaceans, fishes, etc.) predatory animals (echinoderms, mollusks, crustaceans, fishes, etc.) larger predatory animals (mollusks, crustaceans, fishes, etc.)
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).
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