OCG 420 - the squeakquel

What is the largest underwater canyon?

Zhemchug Canyon in Bering Sea

What are trenches?

• Narrow, deep depressions in the seafloor

• Subduction feature at tectonic boundaries

What are canyons?

• Steep walled, sinuous valleys with V-shaped cross sections

• Have large dimensions

• Carved into continental shelfs and slopes

What are the different shapes of submarine canyons?

• Some connect to shelf valleys that are linked to modern rivers

• Some are “headless/blind” = terminate at the shelf

What are 2 ways canyons are formed?

• Subareal formation

• Submarine formation

How are canyons formed from subareal formation?

By ancient rivers, erosion during the last Ice Age when sea level was low

How are canyons formed from submarine formation?

• Turbidity currents

• Slumping

• Earthquakes

• Underwater landslides

What are different characteristics of a canyon as a habitat?

• Steep

• Rough

• Heterogenous substrate

• Fast and complex currents

• Canyon head and walls have rocky outcrops that act as filter feeders

• Sediment accumulates in center of canyon

What do heterogenous substrate include?

• Rocks

• Sediment 

• Carbonate

What species work as filter feeders on canyon head and walls?

• Corals

• Sponges

• Anemones

What animals hang around the center of the canyon where sediment accumulates?

• Fish

• Crustaceans

• Echinoderms

What is the canyon effect?

• Abundance

• Biomass

• Diversity

Why is abundance + biomass elevated in canyons?

• More food here

• Physical structure can trap in organisms

• Local upwelling

• Brings nutrient-rich water to photic zones

• Material gets funneled in from shelf

• Vegetated organic matter sinks into canyons

• Macro algae detritus sink into canyons

How much litter are in canyons?

2x more than in slopes, shelf, and abyssal plain

What do canyons provide?

• Physical structure

• Heterogenous substrate acts as a refuge

• Depth allows dial vertical migration

What is the density like on the canyon of Merenguera Canyon, Spain?

• High density

• There are similar evens in the lower and middle slopes

What is Connell’s Intermediate Disturbance Hypothesis?

Physical processes (such as turbidity current) causes disturbances

What is the productivity level like with moderate disturbance?

High biodiversity

What is the productivity level like with lots of disturbance?

Max disturbances which results in less productivity and lower biodiversity

What is the productivity level with little disturbances?

Less biodiversity and productivity

What determines sediment distribution?

• Distance from land

• Current velocity

• Overlying productivity (column above)

• Smaller sediment travels further'

• Sand, clay, silt

• Diatom (decay from corpses)

What layer of sediment has the highest porosity?

• Flocculant layer, layer at the surface

• (60-80% water)

• It is easier to erode

How do deposit feeders affect porosity?

Increases porosity by pelletizing sediment

How does high porosity affect suspension feeders?

It decreases amount of suspension feeders

What do benthic faunal feed on?

• Rain of organic matter (marine snow)

• Each other

What happens to carbon that falls on the seafloor?

• Need electron donors (organic carbon)

• Need electron acceptors (oxygen)

How do we quantify rates of oxygen demand/consumption?

Sediment community oxygen consumption (SCOC)/Sediment oxygen demand

• Consumption of oxygen by all organisms in community - epifauna, infauna, microbes

What are benthic chambers used to be quantified for?

Sediment community oxygen consumption (SCOC)

What do benthic chambers do?

Seal off communities an monitor concentrations with time

What is the chemistry like as a sediment characteristic?

• Oxic layer on top (is brown)

• Suboxic-anoxic layer below (is black)

Why do sediments become anoxic?

Diffusion of oxygen from water cannot keep up with the pace with aerobic consumption

Where is more organic carbon stored in sediment?

Shallow oxic zones

Where is less organic carbon stored in sediment?

Deep oxic zone

How do abundance and biomass track with organic carbon concentration?

There is less the further you go

What sensors do benthic chambers use?

• Conductivity

• Oxygen

• Turbidity

How do you do sediment profile imaging (SPI)?

• Image taken of seafloor before landing

• Camera prism sinks into the sediment

• Profile image captured

• Lower over ship

What is a large episodic input?

An experiment to test large food falls on benthic communities

What do benthic chambers’ syringes do?

• Inject tracers

• Take samples

What is bioturbation?

• Biogenic transport of sediment particles and pore water

• Changes the chemical + physical properties

How does water bioturbation work?

• Works through ventilation

• Leads to either blind-ended or open-ended

How does particle bioturbation work?

• Gets reworked into different systems

• Either upward conveyors, downward conveyers, or regenerators

What are biodiffusers?

Feed at surface and randomly moving sediment

What are upward conveyors?

Vertically oriented with head down feeding

What are downward conveyors?

Vertically oriented with head up feeding

What are regenerators?

Excavators that dig continuously bring sediment to surface

What are the limits to bioturbation?

• Percent of water decreases with depth, making the sediment harder to burrow through

• Decrease in food with depth

• Decrease in oxygen with depth

• Increase in sulfide toxicity with depth

What is the abyssal plain?

Oceanic crust covered with fine sediment, relatively flat

What % os the seafloor is considered abyssal plain?

~75%

What does terrigenous mean?

Sediment derived from land that goes into the ocean

What are terrigenous sources of sediment?

• RIverine

• Aeolian (atmosphere, wind)

What are biogenies sources of sediment?

• Calcareous

• Silicous 

What are deep-sea sources of sediment?

Authigenic (derived from chemical reactions that happen on the sea floor_

• Manganese nodules

• Phosphorus nodules

What is epibenthic life?

Life on the surface of sediments or rocks 

What is infaunal life?

Life within he sediment

What is benthopelagic/demersal life?

Life that moves between bottom and water column

What is interstitial life?

Life between sand grains (IE microfauna)

What is suspension feeding?

• Passively straining food particles from the water/current

• Relies on water currents to bring them food

• IE deep sea coral + sea pen

What is filter feeding?

• Actively pump water or move appendage

• Filter out food particles

• IE barnacles

What is deposit feeding?

• Ingestion of particles in soft sediment

• Place feeding organ on/in sediment

• Microbial growth on particles enhance nutrition value

• Large intestinal tracts to take in more material than those in shallow water

What is carnivore and predation feeding behaviors in the deep sea?

• Sedentary ambush predators (IE lizard fish)

• Active searchers (IE rattail fish)

• Hyperbenthic crustacean predator (IE tripod fish)

What are seamounts?

• Independent features

• Seamounts rise > 1000 m from seafloor

How are islands related to seamounts?

They are seamounts that rise above the ocean surface

How tall are abyssal hills?

<500 m

How tall are abyssal knolls?

500-1000m

What is a guyot?

• Flat top seamounts

• Flat from erosion when it was above the ocean

What is Mauna Kea?

Tallest mountain on Earth, a seamount

How do subduction zones form seamounts?

Tectonic plates, volcanic arc near subduction zones

How does spreading center work for seamount formation?

Mid-ocean ridge volcanoes

How are seamounts formed?

• Spreading center

• Subduction zones

How were seamounts found?

By satellites, senses the seamounts’ gravitational pulls on water

How are benthic communities on seamounts?

Higher epibenthic megafaunal biomass than those on slopes

How was data collected for seamounts (bluenose warehouse) abundance and distribution?

Acoustic backscatter dats

What do seamounts attract?

• Marine mammals

• Tuna

• Turtles

• Seabirds

• Sharks

Attracted for all the prey near seamounts

How do seamounts function with currents and topography?

• Seamounts trap organisms

• Currents bring nutrients up to the surface

• Strong currents support suspension and filter feeders

How do seamounts work as a habitat?

• Provide physical refuge

• Supports diverse type of organisms

What is a Taylor Column Circulation?

Hydrological structure surrounding a seamount, currents going over the seamounts

May explain high abundance and diversity

What is an upward flow?

Currents collide with base and accelerate upward, carrying cold nutrient-rich toward areas near the surface and provides food for animals living in the vicinity

What is an eddy?

A flat top on seamounts formed from currents

What do eddies do to prey species?

Trap organisms that normally migrate seamounts, easier for predators to eat

What is a downward flow?

Currents that travel up one side of seamount can form rolls and eddies as they move down from the opposite side

What kind of animals live in gravel sediments?

Anemone + ophiuroids

What kind of animals live in basalt seamounts?

Sponges + echinoids

What are seamount currents like?

• Strong currents

• Support suspension (60% of fauna in seamounts) and filter feeders