Marine Geochemistry

why are surface waters at the equator slightly lower in O2
b/c of equatorial upwelling bringing old, respired waters to the surface
What are the three common forms of Nitrogen
NO3 (Nitrate)
NH4 (Ammonium)
N2O (Nitrous Oxide)
What are the two types of phosphate in the ocean?

Orthophosphate, HPO4 2- (90%)

Phosphorus, PO4 3- (10%)

What are the two common forms of Silica in the ocean?
opaline silica (a-SiO2) silacious acid (Si(OH)4) (95%)
Photosynthesis equation
CO2 + H2O + sun + nutrients –> O2 + CH2O
Respiration equation
CH2O + O2 –> CO2 + H2O + nutrients + energy
What reaction explains why phosphate and oxygen profiles are the mirror images of each other?
Respiration; O2 and P are on opposite sides of the respiration equation
What is DOP? Where does it come from?
DOP stands for dissolved organic phosphate
Comes from excretion and degradation products of organisms
What are the main inputs and removals of phosphorus in the ocean?
Rivers are the main inputs of P while P is mainly lost via removal to sediments
Steady State
New Production (input) =Export Production (removal)
What are Alkenones used to detect?
temperature of seawater in which coccoloths grow
Which organisms produce Si exoskeletons?
Diatoms, radiolarians, and siliceous sponges
How does the Si cycle differ from the N & P cycle?
N&P get remineralized, whereas Si is dissolved; since dissolution is a slower process, deepwater [Si] is higher than [P] or [N]

Si is used by siliceous organisms whereas P & N are used by all photosynthetic organism

Si is recycled in surface waters LESS than N or P, but is buried more efficiently than N or P

Why is the concentration of Si in Antarctic Intermediate Water high
Because there are a lot of diatoms and other siliceous organism living in the Antarctic ocean
What is the dominant ocean (sediment) reservoir of C
Calcium Carbonate (CaCO3)
What are the two mineral forms of CaCO3?
Aragonite and Calcite
What is the difference between Calcite and Aragonite?
Calcite is found in deep sea sediments while aragonite is found in shallow sea sediments

Calcite is thermodynamically stable, Aragonite is more soluable

What is the saturation index and how is it related to Ksp

? = [Ca2+][CO32-]/K’sp

Supersaturated: ? > 1

Undersaturated: ? < 1

At saturation, K’sp = 1 and ? = 1

How are the depths of the Lysocline and the CCD related and what are they?
Lysocline = the depth at with an observable change in the %CaCO3 begins

CCD = Calcite Compensation Depth is the depth as which the rate of supply of CaCO3 equals the rate of dissolution of CaCO3 (also called the snow line)

The Lysocline is about 1000-1500m above the CCD

What is the pool size of DOC? of POC?
Pool size of DOC = 685 GtC
Pool size of POC = 30 GtC
What are the main sources of DOC in the ocean?
Organisms (excretion, cell lysis, breakdown of particles, and sloppy feeding)
What eats DOC?
What are the [DOC] in surface and deep waters
Deep water [DOC] = 40 uM Surface water [DOC] = 100 uM
How much DOC is readily identifiable molecularly?
10% in readily identifiable compounds (e.g., amino acids, carbohydrates, lipids)
What is the approximate 14C age of DOC in the N Atlantic and N Pacific

N Atlantic 14C DOC age = 4000 years

N Pacific 14C DOC age = 6500 years

As anthropogenic CO2 enters the ocean, what will happen to [DIC]?
it will increase
Black Carbon
the relatively inert carbon that is formed during incomplete combustion such as in wildfires, e.g., soot, charcoal, and elemental carbon
In terms of 14C age, what is oldest and what is youngest of DOC, DIC, and black carbon in DOC?
DIC is youngest, Black Carbon in DOC is oldest
What are the two main forms of particles that fall into sediment traps in the ocean?
Fecal pellets
Marine snow
What are the two ways to collect POC in the ocean?
1. Traps collect sinking POC and POM
2. Pumps collect suspended POC and POM
Does the concentration of POC vary w/season?
Yes; highest in October, lowest in February, moderate in june/july
what is the flux of POC out of surface oceans? deep oceans?
Flux out of surface: 10 – 200 mg C/m2/day
Flux in the deep ocean: 1 – 20 mg C/m2/day

POC flux decreases with depth

What are the two ways a biomarker can be measured?
gas chronatography
mass spectrometry
What is the pe of oxic seawater
pe = 12.6
what is the pe of organic rich seawaters
pe = 0
Electron Capture
an inner shell electron is captured by a proton to form a neutron

Result is same atomic mass but atomic number is one lower

19K40 –> 18Ar40

Alpha Decay

the unstable nucleus ejects a small part of itself; this particle consists of 2 neutrons and 2 proton

results is atomic mass 4 units larger and 2 atomic numbers lower

238U -> 230Th

Beta Decay
a neutron spontaneously breaks apart into a proton and a high energy positron

results is a nucleus with the same atomic mass and an atomic number one higher

14C -> 14N

What are the major 2 long-lived fission products from nuclear bombs?
Strontium 90 (90Sr) (half life = 29 years)
Caesium 137 (137Cs) (half life = 30.2 years)
Nano Nutrients
Fe, Mg, Zn
Why is the input of P to the deep ocean (B) so low, compared to the amount of P that is utilized during primary production in the surface ocean?
Most of the P utilized during primary production is remineralized in the surface ocean by biological processes and recycled
why is Si productivity more predominant in upwelling/divergence regions?
because there is much less surface water recycling of Si, a greater proportion of Si productivity (as compared with non-Si productivity) must be supported by “new” nutrients (or at least new Si)
What are the reasons to think N is the ultimate limiting nutrient?
N is regenerated more slowly
What are reasons to think that P is the ultimate limiting nutrient?
N2 fixation can alleviate N limitation, but there is no equivalent process to alleviate P limitation
What is higher in the North Atlantic than in the North Pacific?
pH (more basic)
What is higher in the North Pacific than in the North Atlantic?
14C age
Is the concentration of nutrients higher or lower than the concentration of conservative elements in the ocean?
What process is responsible for the change in [DIC] in deep waters as it moves from the North Atlantic to the North Pacific?
In the formation of evaporites, what compound is first to form?
What is the most dominant mineral in evaporites?
Halites (or NaCl)
What element is almost completely removed from seawater during hydrothermal processes?
Where is Si productivity highest?
In regions of divergence or upwelling (Coastal CA, Antarctic, and Equator)
How does the flux of phosphorous change with depth?
It decreases (except at 1500m)
What regions of the ocean are iron poor (Fe limited)?
The Southern Ocean, Equatorial Pacific, and North Pacific (HNLC regions)
Where are nutrient concentrations > 0 umol/L in the surface ocean and why?
In high-nutrient, low-chlorophyll regions (HNLC regions); because there regions are iron limited
How does Ksp change with temperature and pressure?
Ksp increases with increasing pressure
Ksp increases with decreasing temperature
How does CaCO3 solubility change with temperature and pressure
CaCO3 is more soluble at high pressure and low temperature (the conditions of the deep ocean)
How does pH change with depth
it decreases slightly (becomes more acidic)
How does CaCO3 act as a buffer for ocean CO2 systems?
The uptake of CO2 makes waters more acidic, which makes CaCO3 more soluble, and the dissolution of CaCO3 makes waters more basic
how large does organic matter/carbon need to be to qualify as a particle
> 1 micromole
Where in the ocean would there be a minimum flux of POC?
in the gyres, where productivity is low
Define pe
the representation of the activities of electron donors in a solution
Define pH
Representation of the activities of hydrated protons in a solution
What makes Calcite?
foram and cocoliths
What makes aragonite?
pteropods and corals
Atomic Number
number of protons
Atomic mass
= number of neutrons + number of protons
Marine Snow
organic material falling from upper waters to the deep ocean
What is the order in which O2, denitification, sulfate reduction, methane fermentation are used to oxidize carbohydrates in the sediment?
O2 is the first oxidant used, then NO3, then SO42, then CH4
Calcium Carbonate Formation Equation
2HCO3 + Ca > CaCO3 + H2O + CO2
Phosphorous Equation
H3PO4 > H + H2PO4 > 2H + HPO4 > 3H + PO4
Silica Dissociation
Si(OH)4 > SiO(OH)3 + H
What are biomarkers?
A molecule that retains the structure or heritage of its origin
reactivity of half DOC in the surface oceans
How is SiO2 transported to sediments so quickly?
via fecall pellets
What pumps a large amount of water in the ocean?
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