Modeling Studies of the Physical-biological Processes
description
Transcript of Modeling Studies of the Physical-biological Processes
Modeling Studies of the Physical-biological Processes Controlling Spring Bloom Dynamics on Georges Bank:
1-D and 2-D experiments
R. Ji, C. Chen, P.J.S. Franks, D.W. Townsend, E.G. Durbin, R.C. Beardsley, and R.W. Houghton
Compiled from Dr. Townsend’s data
Inter-annual variability of the spring bloom:
Timing Magnitude Location
“Second” bloom in June
Near the front?
Jan
Mar
Apr
May
Jan
Jun
Feb
1997 1998 1999
Chlorophyll a (g/l)
Jan
Mar
Apr
May
Jun
Feb
1997 1998 1999 1997 1998 1999
Nitrate+Nitrite (M) Silicate (M)
Townsend&Thomas, 2002, MEPS
Diatom
Dinoflagellate
Other
Phytoplankton Composition
SeaWiFS data from GOMOOS website By Dr. Andrew Thomas, UMaine
Inter-annual variability of seasonal variation and spatial distribution of phytoplankton and nutrients during spring-early summer time
Seasonal succession of phytoplankton community
Depletion of silicate earlier than nitrogen. Implication of nutrients limitation
“Second” bloom near front area in June, may be corresponding to silicate recovery.
Advection importance. GOM water, SSW, slope water, exchange between central bank and flanks.
What we learned from data?
Model structure
Ammonia Silicate
SmallPhytoplankton
LargePhytoplankton
SmallZooplankton
LargeZooplankton
DetritusNitrogen
DetritusSilica
Predation
Mortality
Remineralization
UptakeUptake Uptake
Dissolution
Fecal
Mortality
Grazing Grazing
Mortality
Mortality
Nitrate
Grazing
Mortality
1
2
3
1-D 2-D 3-D
Seasonal dynamicsSensitivityModel behavior
StratificationFrontal structureCross-section variation
AdvectionEvent level
ECOM-si ECOM-si FVCOM
A
B
1. The central bank in which water is shallow, vertically well-mixed, and relatively self-contained;
2. The mid-bank region characterized by a seasonal tidal mixing front;
3. The outer-flank between the seasonal tidal mixing front and the permanent shelf break front.
1-D
Site A Site B
Biological variables 1-D Model
Site A Site B
Model-Data Comparison 1-D Model
Light1-D ModelSite A
N/Si in diatom1-D ModelSite A
N/Si = 1.5 N/Si = 0.8
Sensitivity analysis
0 0.4 0.8 1.2
VplVpsKpl1Kpl2Kps1Kps2KslRzlRzsRsdRlsSzlSzsSsdSlsGzlGzsGsdGlsEplEpsEzlEzsEdnEdsRnsAfaBetalBetas
/ˆParameter / Parameter
F FS
1-D ModelSite A
What is learned from 1D
What is missing in 1D
Light environment controls the onset of the bloom in the shallow region, while stratification plays a more significant role in the deep region.
Magnitude of bloom is modified by both light and nutrients.
N/Si ratio is an important parameter for the nutrients limitation process and succession of phytoplankton community.
Second bloom in shallow area is not reproduced in the 1D model, although silicate is recovered from later spring depletion with increased water temperature.
The site with deep water didn’t capture the basic pattern of springtime phytoplankton bloom, indicating the significance of advection process.
2-D
2-D model grid
The early spring bloom occurring in the central bank: controlled by biological process associated with light intensity.
The recurrent bloom event during late spring and summer is mainly driven by the seasonal tidal mixing front.
The timing of the bloom on the southern flank is determined by (1) timing of the formation of the tidal mixing front and onset of vertical stratification, and (2) front-ward nutrient flux from the deeper region.
Sectional view
Verticalmixing
Verticalmixing
Critical depth
High NutrientsDeep water
Nutrientsflux
TMF
Verticalmixing
Verticalmixing
light
Critical depth
Wind
Before Stratification
After Stratification
Tide excursion
PMA
Biological field 2-D Model
2-D Model
Sensitivity of bloom to heat flux
What we learn from 2D
What is missing in 2D
The basic pattern of lower level trophic food web dynamics in shallow and deeper area mirrors the site A and site B in 1D model. A unique pattern is developed in tidal mixing frontal zone.
If no impact from advection process, the development of weak stratification is critical for the springtime bloom; wind and heat flux can regulate this process.
The frontal zone is the possible area for the “second” diatom bloom
Like 1D, the deep-water site didn’t reproduce the basic pattern of springtime phytoplankton bloom, indicating the significance of advection process.