Ocean Tracers. From Particles to sediment Thermohaline Circulation Past present and future ocean and climate. Only 4 hours left.

Size: px

Start display at page:

Download "Ocean Tracers. From Particles to sediment Thermohaline Circulation Past present and future ocean and climate. Only 4 hours left."

Cleopatra Clarke
8 years ago
Views:

1 Ocean Tracers Basic facts and principles (Size, depth, S, T,, f, water masses, surface circulation, deep circulation, observing tools, ) Seawater not just water (Salt composition, Sources, sinks,, mixing conservative- nutrient- and particle type elements, gases) Isotopic tracers (stable isotopes,,, Rayleigh distillation, isotopes as mirrors of constituents and transformation, radioactivity,, decay series, cosmogenic and anthropogenic isotopes, radiogenic isotopes). Carbon cycle (carbonate in seawater, hydrolysis, mass action constants, ph, solubility, biological processes, carbon and biological pump, CO 2 flux, seasonality, DIC, CaCO 3 Cycle, Production, dissolution, bicarbonate, 13 C, 14 C, ) From Box Models to GCMs (Continuity equation, fluxes, sources and sinks, Michealson-Menten equation, stationary and dynamic reservoir, isotopic tracers, advection-diffusion models, turbulent laminar flow and diffusion, diffusion length, boundary layers, system boundaries, model complexity, coupled ocean climate models)

2 Ocean Tracers From Particles to sediment ( ) Thermohaline Circulation ( ) Past present and future ocean and climate ( ) Only 4 hours left.

3 Ocean Tracers - From Box Models to GCM s - 1. Basic ideas 2. One Box model 3. A Dynamic reservoir 4. Box model with isotopic tracer 5. Advection Diffusion Models 6. From Box models to fully coupled earth system models

4 Ocean Tracers - From Box Models to GCM s - Conservation law Steady State Production (s) Decay Sink Net influence of the current For radionuclides with short half-life and/or low residence time we can neglect the net influence of the current k i ().

5 Ocean Tracers - From Box Models to GCM s - Diffusive loss of 222 Rn from the ocean Consider 226 Ra -> 222 Rn-> Ra is soluble, Rn is a rare gas and can escape. At depth ( 226 Ra Activity = 222 Rn Activity = 6,7 dpm/100l). Here, only radioactive decay is important and hence k p =0. In the surface oceans mixed layer (of height h) we find A 226 >A 222 (= 4,7dpm/100l). Hence Rn-escape causes a disequilibrium (Rn-loss through diffusion). Using the below equation allows determining k p = 0,067/day. With = 1/k p the renewal time through diffusion become 15 days. k p can also be imagined as v p /h the piston velocity divided the height of the mixed layer. (Broecker & Peng 1982)

6 Ocean Tracers - From Box Models to GCM s - Assume the mother nuclide being in stationary condition

7 Ocean Tracers - From Box Models to GCM s - Bab al Mandab Tor der Tränen

8 Ocean Tracers - From Box Models to GCM s - 15 years Surface water 1. DIC deep = DIC surface 2. neglect radioactive decay 3. Assume step function for surface 14 C rise due to arrival of bomb- 14 C. k i = 1/40 a ( 14 C) Deep water = 40a residence time of the red sea

9 Ocean Tracers - From Box Models to GCM s - C varies within dv due to production, particle scavenging, destruction, and water movement

10 Flow only in x direction. F e = F x dy dz (only first order considered) V = constant What is the physical nature of fluxes?

11 On first order this simple description holds for a laminar flow pattern in x direction where closely related fluid parcels have parallel direction and similar speed. Reality is of course more complicated leading to turbulence at any scale leading to virtually uncorrelated velocity fields.

12 Meandering Golf Stream with a general northward advection at 100 cm /s flow speed and large scales eddys detaching with partly 1. order of magnitude less speed. Regular movements => advection Turbulent movement => diffusion

13 Ocean Tracers - From Box Models to GCM s - Within the time dt a fluid particle carries its concentration along a path in x-direction with u dt. And the surface A = dy dz is passed by a volume u dt dy dz. Thus, the tracer quantity carried across a surface during the time interval dt is equal: dq = C u dt dy dz F = dq / (dt dy dz) = C u The flux is defined as quantity per time and surface [g / s m 2 ]

14 . Ocean Tracers - From Box Models to GCM s - Recall Ficks law F = D dc dx Molecular diffusion The dimension of D is cm 2 /s? Gaz Molar mass Diffusion coefficient (10-5 cm 2 /s) at 0 C at 25 C He 4 3,0 5,8 O ,2 2,3 CO ,0 1,9 Rn 222 0,7 1,4

15 Ocean Tracers - From Box Models to GCM s - D/dx has the dimension of velocity cm/s v p is called the piston velocity imaging two pistons driving diffusion through up and down movement causing diffusion with a characteristic time constant t. v p is called the piston velocity imaging two pistons driving diffusion through up and down movement causing diffusion with a characteristic time constant t.

16 using a mean distance of x m = dx/2 yields x m = Dt/2 in chemical oceanography molecular diffusion plays a major role limiting the exchange of gases between ocean and atmosphere

17 Double diffusive turbulence in sheared oceanic flow Temperature and Salinity diffuse at different rates William D. Smyth, Satoshi Kimura College of Oceanic and Atmospheric Sciences, Oregon State University

18 turbulent diffusion is described equivalent to molecular diffusion but K >>> D To solve mass balance equations in ocean box models mostly turbulent diffusion coefficients are used and solely for gas transfer does molecular diffusion play a key role F = K dc dx dc dt = K d2 C d 2 x taking all together the mass balance equations can be written in the form dc dt = d dx dc K dx dc u dx + s p

Ocean Tracers - From Box Models to GCM s - Transit System / Steady State F in = F out but C in C out Advective System Model with transformations Coupled models need to solve the

19 Ocean Tracers - From Box Models to GCM s - Transit System / Steady State F in = F out but C in C out Advective System Model with transformations Coupled models need to solve the diffusion advection equation in 3 dimensions to estimate the transport of water and constituents, which is generally done through parameterization of an initial state and numerical approximations

20 Ocean Tracers - From Box Models to GCM s - John Shepherd School of Ocean & Earth Science Southampton Oceanography Centre

21 Claudia Kubatzki and CLIMBER-team Potsdam Institute for Climate Impact Research (PIK)

22 W. Broecker The simplest ocean model 2 Boxes Fluxes of water and constituents.. Retrieves mass balances, residence time 1D Model (z)

23 Zonally average models 2D (z, Latitude)

25 Hadley CM3

26 Fully coupled ocean atmosphere Earth system model

27 From Particles to sediment Sources Ocean volume ~ 1, m 3 With roughly t of particulate matter.. thus about mg of particles per 1000 l sea water? Primary production particulate matter discharge aerosols

28 From Particles to sediment Cycle of particles C. Jeandel 1998

29 From Particles to sediment Some major particle types

30 From Particles to sediment Seasonality Punctuated events

31 From Particles to sediment Seasonality Punctuated events

32 From Particles to sediment Seasonality Punctuated events

33 From Particles to sediment Sampling techniques In-Situ Pumps Sediment traps Plankton tow Sediment coring and drilling Video Profiler Light Transmission

34 Jaques Costeau Le Monde Du Silence Photo of a resonant layer at 300m depth. Zooplankton hidding at depth

35 From Particles to sediment New tools

36 From Particles to sediment Image processing.. 5mm Copepods Radiolarians Phaeodarians

37 From Particles to sediment Types Particles: - Small particles and colloids <0,5µm: measurable through light transmission. Sinking speed w p ~ 300m/a - Large particles > 50µm: ~1% of total abundance with sinking speeds of w p ~ m/d A good correlation between video profiling and sediment trap data is obtained, but the spatial and temporal variability of large particles largely exceeds the one of small particles. - All the rest

38 From Particles to sediment Processes Aggregation and disaggregation with organic carbon being the glow for particles. The settling velocity w p determines the (de)coupling between surface and deep ocean (how can surface production be related to deep water particles which may have an age of several weeks or months?) In first order the Stock s law can be used to determine the settling velocity: Frictional force F d on the sphere is balanced by the excess force F g due to the difference of the weight of the sphere and its buoyancy, both caused by gravity

39 From Particles to sediment Processes Baltic Sea particules.

40 From Particles to sediment Observations Video profiler Sediment Traps Stemmann et al (DYFAMED site Med. Sea)

41 From Particles to sediment Observations Light transmission Mc Cave et al. DSRII 2001

42 From Particles to sediment Organic matter flux The annual amount of organic matter production in the ocean is about 60*10 15 g Carbon (60Gt), but only 10% survive re-mineralization. In the open ocean about 1% organic carbon reaches the sea floor, but solely 0,1% survive re-mineralization within the sediment! What does this imply for sediment accumulation rates in the deep center of the ocean gyres? (A) (B)

43 From Particles to sediment Organic matter flux Free floating (buoyant) sediment traps Martin et al Excluded in B) (A) (B)

44 From Particles to sediment Organic matter flux Druffel et al. 1992

Offshore monitoring for geological storage

Offshore monitoring for geological storage Dr Douglas Connelly National Oceanography Centre University of Southampton Waterfront Campus Southampton dpc@noc.soton.ac.uk IEAGHG Taking stock of progress and