1. 1. Updates on 2D model results
McGillicuddy, D.J., Lavelle, J.W., Thurnherr, A.M., Kosnyrev, V.K. and L.S. Mullineaux. Larval dispersion along an axially symmetric mid-ocean ridge. Submitted, Deep-Sea Research I.
2. Toward a conceptual model of the secondary circulations on an axisymmetric ridge?
3. Initial 3-D particle tracking simulations

2. 2-D model currents: May-Nov 1999
Zonal Meridional Vertical
Mean
Standard
Deviation

3. Flank currents: comparison with observations
LADDER Bottom-mounted ADCP
(Andreas Thurnherr)
Time-mean:
Nov 2006 – Nov 2007
Simulated currents:
May-Nov 1999

4. Time-series of simulated currents z=2500m, ±20km of crest
Zonal Meridional Vertical

5. Time-dependent particle release
Sept-Oct animations
10 mab: plan view
10 mab: x-z
225 mab: plan view
225 mab: x-z

6. Particle Positions After 30 Days: Probability Density Functions

7. Trends in larval retention
(1 km bin on ridge crest)

8. Time-mean PDFs as a function of depth and precompetency interval

9. Comparison with Marsh et al. (2001)
Dec 1999 – April 2000
Current
175mab
Example
trajectory
Dispersal
distance
Retention,
dispersal
vs. time
“In the eight-month current profile
from April 1999 to December 1999,
the longest dispersal distance SSE
along-axis was only 54 km.”
Assumptions
Spatially uniform currents
100% mortality of larvae
transported beyond 25 km
of ridge crest
Considered all larvae within
25 km of ridge crest at the
end of their larval period to
be survivors

10. Comparison with Marsh et al
Comparison with Marsh et al. (2001) Particles within ±25km after 26 days
Marsh et al.: Dec 99- Apr 00
This study: May-Nov 99
It is important to note that the Marsh et al. study used a current meter record from a different time period (December 1999 to April 2000) than that used herein (May to November 1999). In comparing the two records, Marsh et al. found that the later time series yielded longer dispersal distances than the earlier record used in the present study. Therefore, were the comparison between these two approaches to be carried out using the same current meter record, the differences in dispersal would likely be even larger.

11. Conclusions Retention is sensitive to vertical position
3-fold variation in time-mean retention
range: 1% (10mab) to 3% (225mab)
Retention is time-dependent
up to 10-fold variation in monthly mean retention
Dispersal distance is sensitive to vertical position
10 mab: ±200km along-ridge
225 mab: ±100km along-ridge
Flank currents play a major role in larval dispersal

12. Hypotheses All else being equal…
-- Species with passive larvae would be the first to re-colonize a new area (longer dispersal distances)
-- Species with a balloonist larval stage can achieve a self-sustaining population with lower fecundity than those with a passive larval stage (higher retention)

13. 1. Updates on 2D model results
2. Toward a conceptual model of the secondary circulations on an axisymmetric ridge?
3. Initial 3-D particle tracking simulations

14. 2-D model currents
Zonal Meridional Vertical
Mean
Standard
Deviation

15. Currents in the EPR system
Oscillatory flow enhances vertical mixing.
Vertical mixing reduces stratification: isopycnals dome updward above the ridge and plunge downward below the ridge.
Displacement of the density surfaces leads to strong flank currents in approximate geostrophic balance.
There is a secondary circulation: mean downwelling is fed by horizontal convergence at the top of the cold dome, and divergence at the crest.
What drives this secondary circulation? What balances the cross-isopycnal buoyancy fluxes?
Oscillatory flow

16. Animations of hourly variations in the temperature field
2 May - 20 June
20 June - 9 August
9 August - 28 September
28 September - 21 November
C.f. Andreas’ density cross-sections from LADDER 1-2-3

17. 1. Updates on 2D model results
2. Toward a conceptual model of the secondary circulations on an axisymmetric ridge?
3. Initial 3-D particle tracking simulations

18. Particle Tracking with the 3-D Model
10mab
75mab
125mab
175mab
225mab

19. Particle depth distributions
10 mab
75 mab
125 mab
175 mab
225 mab

20. Active Vent Sites 1 Biovent
2 Bio1 Tica EastWall M MusselBed Perseverance Q Riftia RiftiaField RobinsRoost RustyRiftia
3 AlvinellidBlanket AlvinellidPillar Bio9 Bio9+ Bio9++ BM119 BM141 BM82 BM89 Io P Ty
4 Choo-Choo TubeWarmPillar Y
5 TevniaHole
6 V
7 A J T
8 Hot8 L
9 B
10 D
11 K DyeRelease
12 PBR600
Depth (m)

21. Population connectivity: 10 mab, Tp=5 d
Source “effectiveness”
Group 3
Group 2
Group 1
Destination “attractiveness”
Relatively higher connectivity within the northernmost 2 groups of vents, which is expected given their proximity.
Structure within/between groups:
1 reseeds itself but little impact on others
2-5 interconnected within group 1, but do not seed group 2 or beyond
group 2 interconnected within itself and group 1; asymmetry: group 2 feeds group 1 but not vice-versa.
More isolated vents to the south: can feed northern vents, but self-sustenance is the most likely.
Source effectiveness: sum the rows to compute the fraction of particles release from each site that settle in a suitable environment; in this scenario, the two vents at the midpoint between the northern 2 groups are the most effective in feeding settlement.
Destination attractiveness: sum the columns to compute the fraction of the total number of particles (from all sites) that settle on each site. The N-S gradient in attractiveness is presumably related to mean flow being mostly northward during this particular time period.
Inspired by Mitarai et al. (2009)

22. Depth of particle release
Precompetency period Tp

23. Future Directions
Generate more robust dispersal statistics for the LADDER era
[requires yearlong 3-D simulation]
Implement behavior more explicitly
Make more direct comparison with larval observations
Dynamics of secondary circulation in 2-D model?