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Flashcards in Chemical Oceanography Deck (85):
1

P:N:C:O2

1:16:106:153

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Nitrate

NO3 ^-

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Phosphate

PO4 ^ 3-

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ocean circulation

~1000yrs

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least reactive major ion

Cl-

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main barrier to ocean mixing

density difference (hence 2 box model)

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Ammonia

NH4+

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Average mix layer

~70m

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Anoxic waters have

higher burial (recall fish farming)

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Largest inputs and outputs

mixing and particle flux >> river input, burial

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(–) AOU

supersaturation

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Nitrite

NO2-

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In a CaCO3 dominant system

surface has decreased Alk,
decreased [CO3 2-]
pH lower
fCO2 higher
atm CO2 higher

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NH4 comes from

respiration product

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what happens to NH4 in surface

converted to NO2, NO3 (only in aerobic/oxic zone)

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local surface max in NH4

lag in the conversion from
respiration –– NH4+ –– NO2- –– NO3-

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Nitrification

NH4 + O2 –– NO2- –– NO3-

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Nitrogen Fixation

N2 ––– NH4+
N2 gas from the atmosphere
requires high Fe

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expected NH4+ profile

low [ ] in surface water - possible small max from respiration
major increase is after o-a boundary

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expected NO3- profile

[low/0] right at surface (productivity)
increases throughout surface layer, fairly high max ~1000m (respiration)
anoxic - decreases back to 0 toward o-a boundary
open ocean - remains ~ stable with depth

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Expected NO2- profile

similar to NO3- but much smaller peak
small peak in oxygen layer from nitrification processes

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high N2

denitrification

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Conservative ions

only affected by evaporation and precipitation
no big fluctuations with depth
[ion] : seawater S remains ~constant
Mg, Na, Ca, Cl-

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Gases

affected by T, S, P, f, reactivity
increase with depth (lower T), except O2

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Bioactive elements

affected by primary production, respiration, remineralization
P, N, Fe, O2

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Trace metals

Very low concentrations
Mg, Fe, Co, Ni, Cu, Zn, Cd

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Oxygen profile without biology

controlled by T like other gases
increase with depth

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Oxygen along thermohaline

depleted
successive losses from respiration

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AOU

[O2]equil – [O2]meas
Apparent Oxygen Utilization
amount respired
oxygen deficit due to respiration
~ opposite to oxygen curve

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typical O2 profile

minimum above 1000m (respiration)
increase after 1000m (horizontal advection from O2 rich high latitude (cold) waters)

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Ventilation impact on O2, AOU

larger ventilation (age, older)
lower O2
higher AOU

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OUR

Oxygen Utilization Rate
mean respiration rate in the water parcel since it left the surface
AOU / Age
high at surface, decrease with depth

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AOU profile

low at surface
max at O2 min (~500-1000m)
decrease with depth

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Oxygen minimum occurs

medium age
medium respiration

35

Carbonate weathering reactions

CaCO3 + CO2 + H2O –– Ca2+ + 2HCO3-
2HCO3- + Ca2+ –– CaCO3 + CO2 + H2O

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low [surface nutrient] affects on fCO2

low [surface nut.] = low fCO2
high P flux –– low [nut.] –– low C (by RKR) –– low DIC –– low CO2 –– low fCO2

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high [surface nutrients], fCO2

high DIC = high fCO2

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Phosphate characteristics

enriched along thermohaline
bioactive, typical bioactive curve
high in S ocean (HNLC)
controlled by photosynthesis and respiration

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DIP_preformed

Preformed = Total – Respired
(DIP_T) – (r_P:O2 x O2_respired)
(DIP_T) – (r_P:O2 x AOU)
Preformed phosphate
portion of P advected to deep irrespective of respiration

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DIP respired

= AOU x (P/O2)
i.e. r_P:O2 x AOU

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Phosphate, Nitrate curves

low at surface (productivity)
increase to a max at ~1000m
decrease with further depth, then ~stable in deep waters with no more respiration occurring

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Nitrate characteristics

Bioactive, typical bioactive curve
extra processes not seen in phosphate
controlled by photosynthesis, respiration (dominantly)

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DIN_preformed

= DIN_T – (r_N:02 x AOU)

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Nitrogen cycle in the surface

NO3 – NH4 –> (photosyn.) Org N
OrgN – NH4 (respiration)
Org N particle flux out of surface

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nitrogen cycle in the deep

P flux -- Org N to the deep
Org N ––(respiration) NH4 ––(nitrif.) NO3
even deeper, anoxic waters
NO3 / Org N –– N2 (denitrification)

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N*

DIN – 16DIP
how does [N] differ from the expected P:N ratio?

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+ N*

N is greater than 16P
Nitrogen fixation likely occurring (adding N)

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– N*

N is less than 16P
Denitrification likely occurring, removing N
**must be low O2 waters

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typical North Atlantic N*

N* +++
high Fe input which is a requirement for N2 fixation

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N* Eastern Equatorial Pacific, Arabian Sea

N* –––
low oxygen zones

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Preformed nutrients helpful for

separating water masses

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Denitrification dependent on

O2 only
independent of [N,P]

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AABW

HNLC - high preformed nutrient, low chlorophyl
Fe limited
low CaCO3 precipitation -- high Alk
extremely cold (hence, dense)

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Atlantic characteristics

N = deep water formation, extremely Saline
~2X S of N Pacific (gulf evaporation)
Generally higher N:P than P
High Fe - Sahara
multiple water sources - AABW, AAIW
harder to see DIC, Alk changes along thermohaline b/c of water mass intrusions

55

AAIW

warmer, less dense than AABW, NADW
spreads out at ~1000m

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Alkalinity =

[HCO3-] + 2[CO3 ^2-] + [B(OH) ^4-] - [H+]
95% of seawater alk =
[HCO3-] + 2[CO3 ^2-]

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Alkalinity characteristics

measurable, accurate, not affected by T, P, k (gas exchange)
main effects from CaCO3 precipitation/dissolution
more soluble at depth (P, 'easier' to be small ions)
primarily affected by biology

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AOU down isopycnal

increases (respiration)

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[P] down isopycnal

increased (respired)

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O2 down isopycnal

decreased (used up in respiration)

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∆Alk from 1mol CaCO3 dissolution

increased 2mol

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Alkalinity profiles

Atlantic- roughly constant with depth, S Atl is higher
Antarctic - roughly constant
Pacific, Indian - increases with depth (thermoh.)

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Pacific characteristics

higher DIP, DIN, DIC, Alk than Atl (more productivity, ventilation)
Deep P_pre ~uniform, 1 water mass
lower [CO3 ^2-], pH
higher fCO2

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DIC =

[CO2] + [H2CO3] + [HCO3-] + [CO3 ^2-]

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Bicarbonate system

CO2atmos ⇌ CO2ocean ⇌ H2CO3 ⇌ HCO3- ⇌ CO3^2-

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pH =

-log[H+]

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fCO2 =

[CO2] / K

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estimating change in carbonate

∆Alk - ∆DIC ≈ ∆[CO3 ^2-]

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increase in DIC, constant Alk

decrease in CO3 ^2-
decrease in pH
increase in fCO2

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salinity normalized DIC

= (DIC / S) * 35

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Increased Alk, constant DIC

bigger ∆Alk – ∆DIC
higher [CO3 ^2-]
higher pH
lower fCO2
less atmospheric CO2

72

Biologic pump

particle flux
relating biological processes, [nutrient], DIC, Alk

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P:N:DIC:Alk

dependent on OM:CaCO3, using 3.5
1:16:136:44

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∆Alk from 1mol Organic Matter respiration

decrease 16/106mol
decrease 0.15mol

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∆DIC from 1mol CaCO3 dissolution

increase 1mol

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O2 profile Atlantic vs. Pacific

Pac- much lower concentration at minimum (higher productivity)
deeper, longer O2 minimum

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pH changes with constant DIC, varying Alk

increase Alk = increase pH
non linear

78

∆DIC from 1mol OM respiration

1mol increase

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CO3 ^2- changes with constant DIC, varying Alk

increase Alk = increase CO3 2-
~linear

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change in fCO2 with varying Alk, DIC constant

increase Alk = decrease fCO2
non-linear

81

AOU profiles, Atlantic vs. Pacific

Pac. - deeper, longer, higher max, correlates w/ O2 profile
higher productivity

82

pH changes with varying DIC, Alk constant

increase DIC = decrease pH
Alk - DIC is smaller
non linear

83

CO3 2- change with varying DIC, alk constant

Increased DIC = decreased CO3 2-

84

fCO2 change with varying DIC, alk constant

increased DIC = increased fCO2
non-linear

85

Seasonality affects on nutrients

N, P surface concentrations highest in winter, lowest in summer
minimum lags spring phytoplankton blooms