Dear Professor Ernst,

You has put very interesting question, thank you.

I have no answer on your question but from my current knowledge (I studied flows theoretically and experimentally almost fifty years) follows that your question can be really separated on several parts:

What is general structure of multicomponent convective flows in flowing stratified environment?

Do larvae have "chemically sensitive sensors" which effect hydrodynamics of specimens?

How can larvae actively govern its behavior in marine environment?

Up to my knowledge, no one of the questions have no complete answer now but they can initiate constructive experimental and theoretical studies.

Short comment on questions.

Almost all current studies directed to investigate particular component of selected phenomenon in a fluid (homogeneous or non-uniform and stratified). For example, investigations of convective plumes do not include description of environmental structures, which are supposed to be unchanged. Really it is not so. In non-homogeneous fluids there are families of weak flows like zero frequency internal waves, diffusion induced flows and so on which put the information about hydrothermal plume into fine structure of surrounding medium and transport information about plume location and activity on a large distance. Moreover, there is no homogeneous fluid in the environment.

In these structures, the chemical components are separated and accumulates in long lamina, which act as leading guide for active specimen.

As we know from dynamics of neutrally buoyant bodies in the environment, changing the shapes the body can govern its motion in the fluid flows. Additional instrument for locomotion is diffusion induced flows and fluxes produced by metabolism of larva, which exchange by substances with the environment.

The velocity of the processes are slow but they are acting continuously.

So in addition to exploration of current knowledge new more detailed investigations are necessary to develop for searching adequate answer on your question.

Yuli D. Chashechkin

LFM IPMech RAS

Dear Yuli,

Thank you very much for the insights and for all the fluid dynamics studies you have carried out on relevant problems. I agree that typically topographic effects are neglected and that stratified crossflows remain a challenge.

Years ago I carried out an experimental study on turbulent particle-laden jets, plumes and associated gravity currents in crossflows and the intention has been to investigate a partially stratified crossflow. The experiments were in a 25m long, 1m wide and 50cm deep flume tank and we had planned to add a layer of boiling hot water in the working section to simulate the effect of a strong stratification to assess if this affected plume bifurcation as theoretically expected, and to explore the interaction in stronger plume-to-crossflow characteristic velocity ratios. In the end we had plenty to do with the unstratified crossflow and left it at that I am afraid.

In any case I agree that much work remains to be carried out and experiments are certainly feasible and some have been carried out including considering plumes in stratified crossflows.

To come back to my question, I believe there must be relevant work already carried out and relevant data collected in the field. Ambiant current velocity field measurements in the deep-sea have been carried out around hydrothermal plume venting sites but I am not aware of their being analysed with any potential assessment of wake vortex generation in mind. The idea being that ambiant current velocity fields are affected and modified by wake vortex shedding like effects.

This is one reason why I asked the question as I suspect there are datasets out there that could be re-assessed with some of the hypotheses I highlighted in mind.

Another issue is that numerical models of hydrothermal plumes in the main are not able to simulate the full range of dynamical regimes or phenomena. Regarding the latter, this includes plume bifurcation (eg. Ernst et al 1994, 1998) and the generation of wake tornadic vortices. The only numerical modeling I am aware of that comes close to doing the above is from Bill Lavelle and colleagues.

As a result, hydrothermal venting scientists interested in dispersal of larvae in the deep-sea (eg. Lauren Mullineaux and colleagues) may not yet have thought about wake "tornadoes" as a possible solution to this issue of dispersing the larvae without killing them in overly toxic fluids.

The issue of toxicity of plume fluid to various types of larvae is, I suspect, another area of uncertainty ?

So I would have liked to hear from colleagues from the hydrothermal venting community.

Regarding suggestions of how vent mounds and multiple buoyancy sources may play a role in generating extreme hydrothermal plume complexity, you may want to have a look at Ernst at 2000 in EPSL which documented a most complex hydrothermal plume from a shallow water site S of Iceland, the Steinaholl plume.

Best wishes with your essential fluid dynamics research into very complex phenomena,

With kind regards to all,

Gerald

Dear Gerald,

Many thanks for your addition, clarifying the discussed topic.

Generally speaking the problem of fluid mechanics is not only in ignoring the influence of topography, but in ignoring a number of other effects too. The indicator is accuracy of measurements in solid mechanics (10^-14 in navigation) and in fluid mechanics (~ 10% or less). The difference is evidence of the need in quality improvements in the latter.

Another problem - the lack of willingness to conduct open discussions. Between each sub-communities exist high barriers.

Moreover, the organization of scientific life (written application - has received a negative review of colleagues - has written a new application - received a positive decision, furiously scribbled report and new applications - was negative ....) leaves no room for thinking and discussion on general topics.

Returning to the equations of fluid mechanics: I think they also contain something unexplored, that describes the spatial structure of currents, i.e. slow components, which the characteristic time of change are much greater than the characteristic times of the dynamically active component determines the scale of the velocity and length. It seems, the answer to your question lies precisely in the interaction of biological, chemical and thermodynamic structures of natural phenomena, which are affected by active dynamical processes.

For their registration, it is necessary to refine experimental techniques taking into account what parameters in the equations are observable and are real physical quantities, and which are derivative quantities derived from mathematical operations.

And yet, another unexplored question about completeness description and experiment.

However, to pose the question is easier than to find the answers.

With best regards

Yuli

Dear Yuli,

Thank you for sharing your experience and insights.

I hear you are advocating for closer mutli-disciplinary research.

As you are coming from the fluid dynamics community, I'd like to share some of  the experience I have had.

Research focused on hydrothermal vents, all aspects of them has become truly multidisciplinary a long time ago now, so that you may find your happiness through linking with this most active and friendly community.

In the 1990s, I was working in the UK and was hired to focus on the fluid dynamics of hydrothermal plumes with funding for about 5 years (and work for about 7 years) from NERC. The programme was called the BRIDGE programme.

The BRIDGE Community has been a most active one and brought together scientists from all disciplines. This led to considerable advances in understanding of hydrothermal vents as systems and as systems of systems and became an important crucible of frontiers'science.

In the BRIDGE Community our group at Bristol was the main one that contributed to fluid dynamics work on hydrothermal plumes (with BRIDGE funding) in my recollections. There was also one other main  group (Cambridge) which focused on trying to understand the fluid dynamics of growth of vent constructs, and had considerable expertise on hydrothermal plume modelling. Besides you will no doubt be familiar with the DAMTP (Herbert Huppert, Andy Woods, et al), who revolutionized geophysical and environmental fluid dynamics together with relatively few other groups (eg. ANU at Canberra...).

Then there was already too little fundamental fluid dynamics in the mix of hydrothermal plume research which was generally truly exciting nonetheless.

Perhaps this was because hydrothermal vent research was still in the age of discovery of most vent sites on the planet (I believe this is still the case). This has been under the great impetus of colleagues such as Chris German and fairly numerous coworkers who discovered a huge number of sites in a rather short time.

Hence much more work, it is only natural I believe, focused on discovering and documenting all the new vent sites, from all viewpoints. This is also why there is now a considerable repository of datasets which still need to be fully mined by fluid dynamics modellers who may consider teaming up with these pioneers of the deep-sea. A most exciting venture that I recommend.

The BRIDGE Programme is only a part of a much larger programme that was called "Inter-Ridge" which preceded it and continues today. The Inter-Ridge Programme has been funded by NSF in the USA and has brought, just as for BRIDGE, many communities together and greatly contributed to advancing frontiers science and generally Earth Systems science.

If one puts all this together, there is a huge amount of data available today for fluid dynamics modellers. A few modellers have been dedicated to focusing on analyses of such data and I recommend, once again, that you consider contacting these colleagues and contribute your extensive expertise in fluid mechanics to joint ventures.

In the USA, fluid dynamics modelling authorities who have focused on hydrothermal plumes include Kevin Speer, Peter Rona and Bill Lavelle.

In the UK, many colleagues at Cambridge continue to make crucial contributions. You may want to contact Harry Elderfield, Mark Rudnicki and their colleagues. Formerly Steve Sparks has also contributed important modelling aspects with Chris German. 

This could be a starting point for your exploration of potential collaborations, if you will.

Then, there are also in the Inter-Ridge community those experts who have focused on deep-sea velocity field measurements. I was hoping to hear from them. I have no doubt that evidence for "wake tornadoes" around hydrothermal plumes has already been collected long ago, but as I have not been following developments closely enough I cannot recall a particular name. These are also colleagues who may be keen to explore collaborating with you and with other fluid mechanics experts.

Traditionally in the plume in crossflow problem, the focus has been to try and understand how crossflows interact with and disperse plumes. Comparatively little attention has focused on how plumes affect cross-currents and change the whole velocity field. The wake tornadoes are an illustration of what one can find out when considering the latter angle of view.

In fluid mechanics, a classic problem is that of studying the interaction of hard obstacles in crossflows, such as cylinders or tapered cylinders. A turbulent jet or plume in a transverse crossflow is a special case where one can learn from the above provided the compliant nature of the plume is also taken into account.

When such an analysis is considered, one can account for why turbulent bent-over jets or plumes initially bifurcate (Ernst et al 1994, Bull Volcanol) and one can anticipate that bifurcation of hydrothermal plumes is common even though logistically this is difficult to document (eg. Ernst et al 2000, EPSL).

I am curious as to whether colleagues may now have documented more bifurcating hydrothermal plumes in this respect ?

When hydrothermal plumes behave as an obstacle to a crossflow, wake tornadoes are anticipated to occur and this can be regarded as an extension of vortex shedding by cylinders in crossflow to some form of vortex stretching and shedding by compliant tapered cylinders in crossflows.

I am still curious to find out if hydrothermal venting colleagues have considered this and their data accordingly ?

I shall leave you with these further réflexions.

I 'd still love to hear from Inter-Ridge colleagues.

With best regards and kind regards to all,

Gerald