Vertical profiles of elements come in a few flavors

• Increasing with depth• Decreasing with depth• Constant

These correspond to the removal processes

• Biological removal• Chemical removal• Not much removal

Summary: Lecture 2

The “biological pump”

Photosynthesis• Depletion of carbon and nutrients• Production of oxygen

Respiration• Depletion of oxygen• Regeneration of carbon and nutrients

Insights from 2-box model

1) physical supply = biological export(from blackboard)

Ps

Pd

Biological export equals Physical supply (or, What goes down must come up)

Blood Sweat and Tears

• Jazz-Rock band • 1967 – present• Famous for “Spinning Wheel”• Terrible

The First Lawof Chemical Oceanography

A Deep Ocean Clock: 14C

n + 14N 14C + p

14Cinit

14C1/2=5730 yrs

Radioactive carbon created in the atmosphere enters the ocean as 14CO2.

It decays with a half-life of 5730 years, providing a “clock” for the flow of seawater from the surface into the deep ocean.

atmosphere

ocean

“Cosmic Rays”

Ocean circulation can be timed with radioactive “tracers”.

Insights from 2-box model

2) Deep Ocean residence time(from blackboard)

Radioactive Carbon

Surface ~ 6%below standard

Mean deep ocean ~ 10% below surface

(plotted relative to an arbitrary standard)

€

Δ14C =14C

14C std

−1 ⎛

⎝ ⎜

⎞

⎠ ⎟* 1000

Willard Libby

•UCLA Professor of Chemistry•Inventor of radiocarbon dating•Nobel prize in 1960•Married to Leona Woods

(also famous scientist, also UCLA professor, developed first nuclear reactor)

The Second Lawof Chemical Oceanography

The deep ocean is ~1000 years “old”.

Insights from 2-box model

3) Global Ocean Productivity

The elemental composition of Marine plankton

μmol/kg

0

5000

1000

dep

th

1 2 3 4

€

106CO2 +16 HNO3 +H 3PO4 + 78 H 2O

€

C106H175O42N16P +150O2

Alfred Redfield

• Harvard Professor of Zoology• Discovered close relationship between plankton biomass and ocean chemistry(a.k.a. “Redfield ratios”)• Pipe smoker, bowtie wearer

Result: Carbon is exported to deep ocean at ~5x1015 g/yr

Plankton are built of elements in nearly constant proportions.

But what was Redfield made of?

The Third Lawof Chemical Oceanography

Human Stoichiometry

€

106 : H 375O132C 85.7N 6.4Ca1.5P1

103 :S206Na183K177Cl127Mg40Si38.6Fe2.7Zn 2.1

100 :Cu 76I14Mn13F13Cr7Se4Mo3Co1

“The Proportions of Man”Leonardo Da Vinci

How and why are we similar to or different from phytoplankton?

Human ProportionsA chemical view

Human ProportionsA geometrical view

The “biological pump”

Photosynthesis• Depletion of carbon and nutrients• Production of oxygen

Respiration• Depletion of oxygen• Regeneration of carbon and nutrients

A problem with the 2-box ocean

The elemental composition of Marine plankton

(from blackboard)

O2μmol/kg

0

4000

1000

dep

th

100 200 300

Insights from 2-box model

3) Global Ocean Productivity

The elemental composition of Marine plankton

μmol/kg

0

5000

1000

dep

th

1 2 3 4

€

106CO2 +16 HNO3 +H 3PO4 + 78 H 2O

€

C106H175O42N16P +150O2

Introducing Horizontal Variations

To understand this, we need to study ocean circulation!

Surface Phosphate, PO4 (mmol/m3)

rivers

sedimentsf

Reviving Rivers

How many times will a P atom see the abyss?

Ps

Pd

Insights from 2-box model

4) External inputs vs. Internal recycling