EVOLUTION: OCEAN CIRCULATION

CURRENTS AND DENSITY

Currents of major impact on the ocean are profoundly influenced by density differences due to salinity and temperature differences.  The heavier water sinks and the lighter water rises.  Surface currents can be wind driven.  Gravity and inertia impact currents.  At the interface of moving currents, or a current and still water, turbulence and mixing can be induced.

Pure water is most dense at about four degrees centigrade.  So progressively warmer water is usual found from near the bottom to near the surface.  Salt concentration of the water may make the temperature stratification vary in other ways.  For example, Mediterranean Sea water entering the Atlantic Ocean near the Straights of Gibraltar sometimes goes to an intermediate depth based on density level of the ocean of the same density, but with different temperature and salinity.

Most of us are familiar with the affect of the Gulf Stream on climate in Europe, by its movement north along the western Atlantic that veers east and provides milder climates to northern Europe.  A similar current affects climates in the north Pacific.  While such currents catch our attention, one of greater consequence has had a profound affect on evolution as it has no doubt persisted and survived assaults by asteroids, volcanic disruptions, continental drift, and variations in solar radiation.  It involves a cycle of circulation that takes ten thousand or more years to complete - from icy polar water settling to abyssal depths of temperate, sub-tropical, and tropical parts of the ocean where it slowly warms and rises until it ultimately mixes with warmer surface waters and completes the cycle by returning to polar regions via currents and evaporation and precipitation.  A pause in polar ice caps can exceed the ten thousand plus year trip from abyss to sea surface.

                                 A PERSISTENT CIRCULATION PATTERN
polar region                                                  temperate - sub-tropical regions

The visual above is not to scale but indicates the North Atlantic pattern of circulation from polar regions on the left to tropical regions on the right.  Similar but variable profiles would be found in the North Pacific and Southern Ocean region of Atlantic, Pacific, and Indian Oceans.  The flows would diminish and seem to disappear as they meet under tropical waters.

S represents the ocean floor or sediment with a sill regulating flow from (the sometimes ice covered) Arctic Ocean water.  A rise in sea level, or a subsidence of the sill can allow a greater volume of flow to the abyss of the Atlantic.

C represents the cold salt water of high density that sinks to the depths of the ocean of such great volume that the warming water rises slowly, taking ten thousand or more years to mix with the warmer and less dense overlying water.

M represents the oxygen minimum zone separated from W, the warm surface water, by a thinner mixing zone, the thermocline.  The thermocline is identified by rapid change in temperature.  A shallow thermocline may result in more light for photosynthesis penetrating beyond the mixing zone so the oxygen minimum will be somewhat deeper.  Also, storms may produce sufficient turbulence at depths to make the oxygen minimum zone deeper.  The extent of the oxygen minimum zone also responds to organisms living there and bacteria utilizing organic debris settling from the photosynthetic zone near the surface.

W, the warm water is where oxygen is replaced by photosynthesis as well as by diffusion from the atmosphere.

Hurricanes

The thickness of the thermocline is greatly affected by wave action.  Calm seas may have a thermocline within a hundred meters of the surface.  Hurricanes and storms can produce turbulence to make the thermocline much deeper and provide a thicker zone of warm water and heat storage that may prolong or increase subsequent storms.

The H.M.S. CHALLENGER EXPEDITION

The first major oceanographic expedition occurred from late 1873 to early 1876.  One of its many accomplishments was measuring depths, temperatures, and salinity of the oceans.  I had examined part of one of the fifty some volumes of its researches published later that century while I was teaching a marine biology class about a hundred years after the voyage.  I don't know how many years it took me to realize that the temperature profile that I have crudely illustrated above meant that the presence of oxygen and long residence time of the deep water beneath the thermocline meant either extremely low biological activity or very few organisms.

Subsequent oceanographic work has provided more complete coverage of the oceans and greater precision in measurements without changing the basic importance of the early expedition.

The time factor

Sediment cores show the vast percentage of abyssal sediments accumulate very slowly.  That helped me understand the extreme age of some bottom dwelling animals as indicated by their tubes position in sediments.  The embedding in sediments was inferred from the rarity of finding their posterior ends in dredge samples, absence of tube rings on a posterior branch of the fork of branched tubes, and funnel-like rings on some species with rims oriented toward the anterior end (the exposed tentacle bearing ends giving rise to the common name, beard worms, of the Pogonophora).

My paper describing the evidence for the beard worms extreme age -    Engemann, Joseph G.  1968.  Pogonophora: the oldest living animals?  Pap. Mich. Acad. Sci., Arts, and Letters, 53:105-108.   - was reprinted in the final chapter of -    Engemann, Joseph G., and Robert W. Hegner.  1981.  Invertebrate Zoology, 3^rd ed.  Macmillan Publishing Co., New York.  746 pp.  The extreme age concept can be found in several earlier posts of this blog.

The extreme longevity of deep sea animals is part of a circular argument that suggests the slow replacement of the cold deep water of the ocean, which in return, suggests the extreme age of the organisms there.  Fortunately, other evidence is available to augment the invalid circular reasoning.  The most dramatic bit was discovery of unspoiled fruit and sandwich on a lunch recovered from the Alvin submersible research vessel many months after it sank to great depth.  Several studies involving respiratory rates of deep sea organisms show greatly slowed rates compared to comparable organisms of shallow seas.

Evolutionary implications

Some major implications are discussed in numerous past posts.  Two major ones are-

- the error compounded in molecular phylogeny studies (especially establishment of the Ecdysozoa concept), and the unique missing link role that the pogonophorans fulfill.

The permanence of the ocean stratification in tropical through temperate zones has provided stable environments where the extremely slow metabolism resulting from low temperature and immense pressure allowed those that slowly adapted to the abyssal region to survive.  The pogonophorans are one of the most significant, but little known, groups.  Neopilina is an important indicator of molluscan relationships and their annelid ancestry.  Brittle stars are abundant on many areas of the ocean bottom and help us understand the selective pressures giving rise to shallow water relatives.  The coelocanth fish was found at intermediate depths but is a living relative of what is otherwise known from fossils.

Will the enormous area and depth protect marine life there from the assault of a constant flow of debris and chemicals we dump from ships, atmospheric contamination and polluted streams?

Joseph G. Engemann     Emeritus Professor of Biology,  Western Michigan University,  Kalamazoo, Michigan      May 3, 2018

EVOLUTION AND THE SECRET OF THE TREE OF LIFE

THE TREE OF LIFE

The tree of life, as currently accepted by main-stream science, has an unaccounted for error.  It is no secret to you if you have read all my posts, but the molecular phylogeny of major phyla has major errors for lack of understanding long-branch attraction.  Or as I have shown from numerous citations elsewhere, abundant evidence that direct measurement of DNA differences of species is almost certain to produce an erroneous tree-of-life for phyla if it is calculated from those differences.

LONG BRANCH ATTRACTION

Molecular phylogenies are sometimes plagued with the pogonophorans or some other group appearing in some central position in a phylogeny when the researcher is quite certain it should not be there.  They may note that it doesn't seem to belong there, or, I suspect, sometimes they leave it out because they think it is a long-branch attraction appropriate to ignore.  Maybe they just remember not to use the group for an out-group [a group inserted that is reasonably presumed to be outside the cluster being investigated].  The correct solution is to figure out why it happened - something they cannot do without introducing a major variable of molecular clocks all ignore.  I have discussed elsewhere how the nematodes may also have a slower rate of change in their genome and thus produce an example of long branch attraction.

THE POGONOPHORA

The Pogonophora are specialized descendants of polychaete annelids of which the ancient ones are ancestral to all vertebrates via hemichordates and cephalochordates as indicated in Our Evolutionary Lineage (Post  79).    [ http://evolutioninsights.blogspot.com/2014/12/our-evolutionary-lineage.html ]

That post also lists approximate times of origins of groups in that lineage.  From that we can see that the pogonophorans evolved about a billion years ago.  Some are little changed to this day, if they stayed in the abyss, from perhaps 600 million years ago when the hemichordate line branched off from some of the pogonophorans moving into shallower waters.  From hemichordates the cephalochordates branched off, perhaps 500 million years ago.

THE CAMBRIAN

About 500 million years ago the Cambrian began.  Most major phyla had representatives in the Cambrian.  Trilobites were arthropods whose fossils are only found in rocks through the Cambrian to the end of the Palaeozoic.  Arthropods are obvious annelids descendants that have an origin from polychaetes, as do pogonophorans.  Mollusks had a comparable origin from polychaetes.

The stability of conditions in the Cambrian enabled pogonophorans ancestors to migrate to shallower seas and survive following the end of major asteroid bombardment episodes.  As they established themselves in shallow seas, the reduced pressure enabled physiological processes involving diffusion to speed up to a 1,000 times greater speed.  A better food supply also contributed to the process.  The recovery of gut development by the hemichordate descendants accompanied other developments as the worms moved out of their tubes and took on a more active life getting particulate food, mostly by filtration instead of the diffusion on which the pogonophorans had become dependent.

Parallel lines from the polychaete-pogonophora line gave rise to echinoderms and probably some of the lophophorate phyla that also made their appearance in the Cambrian.

CALCULATING THE LONG BRANCH ATTRACTION

We can ignore the fact that pogonophoran tube analysis (in earlier blogs) indicates the individuals can live from 10,000 to a million or more years.  Just taking the pressure differential effect on physiology indicates evolutionary selection is likely to be 1,000 times more rapid in shallow seas than in abyssal ones.

The ancestor that remained and reproduced in the abyss over the past billion years would be expected to have one million nucleotide substitutions in their DNA while a descendant that had been near the surface has 500 million nucleotide substitutions in the past half-billion years.  Another descendant branching off at the same time would also have 500 million nucleotide substitutions in the past half-billion years.

Others branching from the new lines, say one from each line 400 million years ago, each would have 400 million nucleotide substitutions in each of their lines as differences.

THE SURPRISE

Now, the four groups would all have more in common with the pogonophoran that now has half a million changes from the point of common ancestry with the other four groups that each has 500 million changes.

The branching of the new groups would be correctly interpreted from the differences as *800.0 million changes from their nearest relative and *1,000.0 million from each of their more distant pair of relatives, but only *500.5 million changes from the pogonophoran.  The pogonophoran now looks closest to all by the long branch attraction, an artifact of different rates of evolution whether by physiological speed or long generation time, or by both as I think it is.

The closer the groups studied, in a phylogenetic study of relationships, the more likely it is that pogonophorans will not show up as a close relative within a group.  Thus species, genus, and families in an order are unlikely to appear related to pogonophorans unless the study is of pogonophorans.

If you look at the estimated times of origins you can see that terrestrial vertebrate classes had their origins over three hundred million years ago. but most modern orders were likely beginning almost two hundred million years ago.  Nearly the same thing could be said about the insects.  Whereas echinoderms are a more ancient group with classes going back to the Cambrian; they even have several extinct classes.

Until the molecular phylogeneticists calculate a major tree of life taking the above into consideration they will continue to be wrong about their view of relationships of phyla.  They have a lot to contribute if they stop making that error. 

*The numbers used in the examples above are not precise and are only used for a simplified example of the principles involved and are calculated by summing the changes of both ancestral lines from their point of branching.

Joseph G. Engemann     Kalamazoo, Michigan   February 2, 2015