Chapter 2 – The Input of Material to the Ocean Reservoir

Question 1

What are the three major natural sources of material injected into seawater?

Answer 1

The continental crust, the oceanic crust, and the atmosphere

Question 2

What processes mobilize primary material from the continental crust?

Answer 2

Low-temperature weathering and high-temperature volcanic activity

Question 3

What is secondary (pollutant) material mobilized by?

Answer 3

Anthropogenic ‘weathering’ processes, often involving high temperatures

Question 4

What forms does released material take during natural and anthropogenic processes?

Answer 4

Particulate, dissolved, and gaseous phases

Question 5

What are the three principal transport routes for continentally mobilized material to the ocean?

Answer 5

River, atmospheric, and glacial transport

Question 6

Which pathway delivers material most widely across the ocean surface?

Answer 6

Atmospheric transport

Question 7

Which transport pathway is second only to rivers in supplying particulate material to the oceans?

Answer 7

Glacial transport

Question 8

Why is ice transport less important as a source of dissolved material?

Answer 8

Because ice has reduced chemical weathering (being frozen)

Question 9

What are the main oceanic crust processes supplying material to the oceans?

Answer 9

Low-temperature weathering and hydrothermal activity at spreading ridges

Question 10

What is a key hydrothermal contribution to the ocean’s geochemistry?

Answer 10

Dominant supply of dissolved manganese

Question 11

What are the three key questions to evaluate riverine input to the ocean?

Answer 11

(1) What is transported by rivers? (2) What happens in estuarine mixing zones? (3) What reaches the open ocean?

Question 12

What is the dominant chemical signal in river water compared to seawater?

Answer 12

River water is dominated by calcium and bicarbonate; seawater by sodium and chloride

Question 13

What are the main sources of dissolved and particulate materials in rivers?

Answer 13

Rock weathering, organic decomposition, atmospheric deposition, and anthropogenic discharges

Question 14

How is dissolved material in river water operationally defined?

Answer 14

Material passing through a 0.2–1 μm filter (includes colloids)

Question 15

What are colloids and why are they important?

Answer 15

Very small particles (<0.2 µm and >1 nm) with high surface area that significantly interact with dissolved species

Question 16

What are the three end-member types of surface waters in the Gibbs diagram?

Answer 16

Precipitation-dominated, rock-dominated, evaporation–crystallization dominated

Question 17

What cations and anions characterize freshwater and seawater respectively?

Answer 17

Ca²⁺ and HCO₃⁻ for freshwater; Na⁺ and Cl⁻ for seawater

Question 18

What does a high Na/(Na+Ca) and Cl/(Cl+HCO₃) ratio in river water indicate?

Answer 18

Precipitation dominance and possible evaporation effects

Question 19

What types of rocks result in higher weathering products in rivers?

Answer 19

Sedimentary rocks (especially carbonates) over crystalline rocks

Question 20

What environmental factors control river water composition?

Answer 20

Lithology, relief, climate, vegetation cover, and pollution

Question 21

What is the order of weathering intensity among rocks?

Answer 21

Evaporites&raquo_space; carbonate rocks&raquo_space; crystalline rocks

Question 22

What is the primary control on the major ion chemistry of rivers?

Answer 22

Rock weathering

Question 23

How do mean annual runoff and dissolved solids correlate?

Answer 23

Higher runoff leads to lower concentration but higher flux of dissolved solids

Question 24

What are trace elements in river water defined as?

Answer 24

Elements with concentrations <1 mg/L (often much lower)

Question 25

What affects trace metal solubility in river water?

Answer 25

pH, complexation with organic matter, and adsorption to particles

Question 26

Which trace elements are highly mobile (ARD/AUC ratio ≥ 1)?

Answer 26

Chloride, calcium, and molybdenum

Question 27

Which trace elements are poorly mobile in river systems?

Answer 27

Aluminium, lead, and iron

Question 28

What human activities affect trace metal concentrations in rivers?

Answer 28

Mining, agriculture, industry, urban discharges, and atmospheric deposition

Question 29

What are the two main types of atmospheric inputs to the ocean?

Answer 29

Wet deposition (rainfall) and dry deposition (aerosol particles)

Question 30

What is the principal mechanism of atmospheric transport?

Answer 30

Long-range transport via the wind system

Question 31

What type of material is most efficiently transported by the atmosphere?

Answer 31

Fine particles and gases

Question 32

What are the primary sources of atmospheric aerosols?

Answer 32

Sea spray, continental dust, volcanic emissions, biomass burning, fossil fuel combustion

Question 33

How does particle size affect atmospheric transport?

Answer 33

Smaller particles travel farther; large particles settle quickly

Question 34

What is a key natural source of mineral dust?

Answer 34

Arid and semi-arid continental regions

Question 35

What factors influence the chemical composition of dust?

Answer 35

Source region lithology and atmospheric processing during transport

Question 36

What is sea-salt aerosol primarily composed of?

Answer 36

Sodium chloride, with smaller amounts of other seawater-derived ions

Question 37

What processes generate sea-salt aerosol?

Answer 37

Bubble bursting and wave action at the ocean surface

Question 38

What is the significance of non-sea-salt sulfate in marine aerosols?

Answer 38

It indicates sources like volcanic activity or oxidation of marine biogenic gases (e.g., DMS)

Question 39

What is the dominant anthropogenic aerosol component over oceans?

Answer 39

Sulfate derived from fossil fuel combustion

Question 40

What distinguishes marine from continental aerosols?

Answer 40

Marine aerosols are typically coarse and salt-rich; continental aerosols are more variable and often fine-grained

Question 41

What role does rainfall play in atmospheric deposition?

Answer 41

It scavenges both soluble gases and particulate matter from the atmosphere

Question 42

How does pH affect rainfall chemistry?

Answer 42

Low pH (acidic rain) enhances dissolution and transport of trace metals

Question 43

What is the significance of dust inputs for ocean biogeochemistry?

Answer 43

Dust supplies key nutrients (e.g., Fe, P) to surface ocean waters

Question 44

Why is iron input from dust important in some ocean regions?

Answer 44

Because it limits primary production in high-nutrient, low-chlorophyll (HNLC) areas

Question 45

What happens to dust once it reaches the ocean surface?

Answer 45

It can dissolve, sink, or be transformed through biological and chemical processes

Question 46

What is “wet deposition”?

Answer 46

Delivery of material to the ocean via precipitation

Question 47

What is “dry deposition”?

Answer 47

Gravitational settling or impaction of aerosols onto the ocean surface

Question 48

What is the main geological setting for hydrothermal activity?

Answer 48

Mid-ocean ridges and spreading centers

Question 49

What drives hydrothermal circulation at ridge crests?

Answer 49

Heat from underlying magma chambers

Question 50

What happens when seawater penetrates the ocean crust?

Answer 50

It heats up, reacts with basalt, and is returned to the ocean enriched in elements

Question 51

What are the two main types of hydrothermal fluid outputs?

Answer 51

High-temperature vent fluids and low-temperature diffuse flows

Question 52

What is a "black smoker"?

Answer 52

A high-temperature hydrothermal vent emitting metal-rich fluids that precipitate on mixing with seawater

Question 53

What is a key chemical feature of hydrothermal fluids?

Answer 53

Enrichment in metals like Fe, Mn, Zn, Cu, and depletion in Mg and SO₄²⁻

Question 54

Why is Mg absent in hydrothermal fluids?

Answer 54

Because it is removed during water–rock reactions within the crust

Question 55

What mineral forms when hydrothermal Fe oxidizes in seawater?

Answer 55

Iron oxyhydroxides (e.g., Fe(OH)₃)

Question 56

What is the significance of Mn in hydrothermal plumes?

Answer 56

It remains in solution longer, serving as a tracer for vent activity

Question 57

How do hydrothermal inputs affect deep ocean chemistry?

Answer 57

They influence metal budgets and local geochemical cycling

Question 58

What are the primary controls on hydrothermal input composition?

Answer 58

Temperature, rock type, and water–rock reaction extent

Question 59

How does hydrothermal activity act as both source and sink?

Answer 59

It adds some elements (e.g., Mn) and removes others (e.g., Mg, O₂, SO₄²⁻)

Question 60

What is the global significance of hydrothermal vents?

Answer 60

They contribute significantly to the oceanic budget of some trace elements

Question 61

What is the estimated global flux of hydrothermal water?

Answer 61

Around 10¹⁴ kg/year (10⁵ m³/s)

Question 62

What role do microbial communities play at vent sites?

Answer 62

They utilize chemical energy from hydrothermal fluids (chemosynthesis)

Question 63

Why is hydrothermal iron important for surface productivity?

Answer 63

It can be transported via plume dispersion to distant surface waters, aiding primary production

Question 64

What causes rapid precipitation of metals from vent fluids?

Answer 64

Mixing with cold, oxygenated seawater

Question 65

What is the main goal of comparing fluxes in marine geochemistry?

Answer 65

To assess the relative importance of different material sources to the ocean

Question 66

What are the four main pathways supplying material to the ocean?

Answer 66

Fluvial, atmospheric, glacial, and hydrothermal pathways

Question 67

Which pathway delivers the largest flux of dissolved material to the ocean?

Answer 67

Fluvial input

Question 68

Which pathway delivers the largest flux of particulate material?

Answer 68

Atmospheric dust deposition over wide ocean areas

Question 69

How do glacial inputs compare to other pathways?

Answer 69

Significant for particulate input in polar regions but limited globally

Question 70

Why is hydrothermal input often underestimated?

Answer 70

It is difficult to measure and distributed along deep-sea ridges

Question 71

What element is dominantly supplied by hydrothermal activity?

Answer 71

Manganese (Mn)

Question 72

What complicates the calculation of fluxes to the ocean?

Answer 72

Temporal and spatial variability, and limited data for some regions

Question 73

What are the units commonly used to express fluxes?

Answer 73

Grams or moles per year (g/yr or mol/yr)

Question 74

What is a key consideration when comparing dissolved and particulate fluxes?

Answer 74

Many elements cycle between these phases during transport

Question 75

How can atmospheric inputs affect remote ocean regions?

Answer 75

By supplying essential micronutrients like iron (Fe) via dust transport

Question 76

What role do shelf seas play in the global material cycle?

Answer 76

They act as reactive zones processing and transforming inputs from rivers and atmosphere