Greenhouse worlds & Oceanic anoxic events

Question 1

What rock type can be used to show anoxic events in the past?

Answer 1

Black shales

Question 2

What are the seasonal cycles like with photosynthesis at present day?

Answer 2

High near equator where strong upwelling
High in NH summer

Question 3

Where are large algae populations likely to be found in the marine environment?

Answer 3

Continental margins due to run off

Question 4

What is the main control on phytoplankton productivity?

Answer 4

Nutrient levels

Question 5

What are the major nutrients needed by phytoplankton?

Answer 5

N
P
Si (diatoms with silica shell)

Question 6

What minor nutrients are needed by phytoplankton?

Answer 6

Fe
Zn
Cu

Question 7

How are phytoplankton supplied their nutrients?

Answer 7

Deep ocean via upwelling
River runoff along coasts
Aeolian dust deposition
Recycling in the upper ocean/mixed

Question 8

Where are algal blooms concentrated depthwise?

Answer 8

In the photic zone (top 100m)

Question 9

What happens to nutrients used by phytoplankton?

Answer 9

Absorbed then when organism dies either eaten or sink to sea floor

Question 10

What is biopump?

Answer 10

Nutrients absorbed by phytoplankton then poo or die and then upwelling brings it back to surface

Question 11

What happens to oxygen levels when phytoplankton release energy form their food?

Answer 11

Oxygen used up and co2 increased (oxygen depletion) creates oxygen depletion zones

Question 12

What is an example of an unnatural anoxic event?

Answer 12

Deepwater horizon 2010

Question 13

What was the cause of the deepwater horizon?

Answer 13

Failure to control oil pressure so well blew out of sea floor

Question 14

How did deepwater horizon cause anoxia?

Answer 14

plume spread out to the west Microbes were eating it and using oxygen this created very low oxygen zones which was worst for larger organisms which need high oxygen level

Question 15

What levels of oxygen is needed for water to be “saturated”?

Answer 15

7-8 mgl

Question 16

Below what oxygen level is water hypoxic?

Answer 16

2 mgl

Question 17

What is hypoxia and anoxia?

Answer 17

Hypoxia- low oxygen
Anoxia - no oxygen

Question 18

What is an example of an area which is always hypoxic?

Answer 18

Black sea

Question 19

What is an example of an area with seasonal hypoxia?

Answer 19

Baltic sea

Question 20

What is an example of an area with temporary hypoxia?

Answer 20

Areas affected by el nino i.e. east south American coast

Question 21

What are the causes of hypoxia in modern oceans?

Answer 21

Limited connections to the open ocean
High nutrient loading from land
Highly stratified

Question 22

How can stratification affect oxygen levels?

Answer 22

If highly stratified by temp (warm on top cold below) there will be very little mixing

Question 23

How many “dead zones” are there and what area di they occupy?

Answer 23

405
250,000 sq km

Question 24

What is the future threat of warming temp to hypoxia?

Answer 24

Increased air temp will increase surface water temp intensifying stratification

Question 25

How can carbon be used to analyse past conditions?

Answer 25

lighter c12 will be taken up more readily
More C12 = negative c13 and vice versa

Question 26

How does ocean anoxia affect carbon levels?

Answer 26

C12 in organisms sinks and locked in sediment as black shale resulting in + C13 value

Question 27

What is the Selli event?

Answer 27

Oceanic anoxic event 1a
Early Aptian = ~120 ma

Question 28

What were the outcomes from the Selli event?

Answer 28

Widespread black shale deposition across the Tethys
Large positive δ13 C excursion;
Long duration ~1 Ma
Increase in high-nutrient phytoplankton groups

Question 29

What is the Bonarelli event?

Answer 29

Oceanic anoxic event 2
Age: Cenomanian/Turonian

Question 30

What is special with mesozoic oceans?

Answer 30

Early opening of Atlantic
Restricted Tethys seaway -> limited ocean circulation & ventilation

Question 31

What is special about the mesozoic climate?

Answer 31

Period of global warmth (~ice free poles)
Warm polar and high latitude regions
Oceans that are warm, sluggish circulation and low in oxygen

Question 32

What is the temp gradient between the poles and tropics like in the mesozoic?

Answer 32

Very weak gradient so little circulation

Question 33

Why is there increased burial of organic carbon in oceanic anoxic events?

Answer 33

Reduced oxygen content in deep ocean during OAEs ->
Less organic matter break down in deep ocean sediments by bacteria and animals that need oxygen ->
More organic carbon being buried rather than “eaten”

Question 34

What was the source of CO2 for the Selli event?

Answer 34

Ontong Java Plateau volcanism

Question 35

What are oceanic anoxia events often linked to?

Answer 35

Large igneous provinces

Question 36

How can anoxia affect evolution?

Answer 36

Belemnites were originally deep water but OAE forced them to live in surface waters where they evolved to live there as Oxygen levels returned their habitat radiated form surface to deep water