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Flashcards in Chemical Oceanography Deck (85)
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31

Ventilation impact on O2, AOU

larger ventilation (age, older)
lower O2
higher AOU

32

OUR

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

33

AOU profile

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

34

Oxygen minimum occurs

medium age
medium respiration

35

Carbonate weathering reactions

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

36

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

37

high [surface nutrients], fCO2

high DIC = high fCO2

38

Phosphate characteristics

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

39

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

40

DIP respired

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

41

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

42

Nitrate characteristics

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

43

DIN_preformed

= DIN_T – (r_N:02 x AOU)

44

Nitrogen cycle in the surface

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

45

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)

46

N*

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

47

+ N*

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

48

– N*

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

49

typical North Atlantic N*

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

50

N* Eastern Equatorial Pacific, Arabian Sea

N* –––
low oxygen zones

51

Preformed nutrients helpful for

separating water masses

52

Denitrification dependent on

O2 only
independent of [N,P]

53

AABW

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

54

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

56

Alkalinity =

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

57

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

58

AOU down isopycnal

increases (respiration)

59

[P] down isopycnal

increased (respired)

60

O2 down isopycnal

decreased (used up in respiration)