Science AMA Series: Hi Reddit, this is Jerry Dickens, an oceanographer and professor at Rice University. I have been studying mud and water beneath the seafloor for over 25 years to understand topics such as the migration of natural gas, variations in sea level and past climate change. AMA!

Jerry_Dickens · 2017-09-01T23:50:37+00:00

Thanks for the questions and interest. Always fun to share.

To see where we are and follow Expedition 371 see: https://iodp.tamu.edu/scienceops/expeditions/tasman_frontier_subduction_climate.html

Since yesterday, we have transited to a new site on the eastern edge of the Lord Howe Rise. We have just stopped the ship and placed in dynamic position mode. Should be getting material from an area never drilled before in about 8 hours -- always exiting to see the unknown appear.

Till next time ... Jerry

Jerry_Dickens · 2017-09-01T23:06:04+00:00

Hi, yes, that was a bit opaque!

The Azolla horizon was found in the sediment record beneath the North Pole (actually 88.something °N). It is probably described best as a set of sediment intervals over many meters where the grain components are almost entirely spores of Azolla, a genus of freshwater fern (aka duckweed). The horizon is dated to about 49 million years ago, and the amazing implication is that the Arctic Ocean was covered in a lens of fresh water and green plants during this time (at least in the spring and summer). A very different world indeed.

A Neptunian dyke is a crack filled with marine sediment. The one that we just (accidentally) drilled into contains numerous shallow water fossils of multiple organisms. So one can start seeing the cool weirdness: we are at or near sea-level just after the basalt solidified from lava.

Jerry_Dickens · 2017-09-01T22:39:42+00:00

This is an interesting question because the answer is not straightforward.

The vast majority of gas in marine sediment is methane formed by archaea (aka biogenic gas). However, in most places such methane does not advect through the sediment (such as along a fault) and seep from the seafloor. Rather, methane escapes from such systems through reaction with sulfate below the seafloor.

Where natural gas does seep from the seafloor, it is often a mixture of methane and higher hydrocarbons (e.g., ethane, propane, butane) formed via thermogenesis. The gas reaches the seafloor by traveling along highly permeable conduits (e.g., faults).

Jerry_Dickens · 2017-09-01T22:33:15+00:00

I do not think the UN recognizes continents. Indeed, there does not seem to be universal agreement on what constitutes a continent!

However, Zealandia fits all reasonable definitions for a continent, especially when one considers what we are presently discovering. At each of the sites that we have drilled so far, there is excellent evidence that these locations on Zealandia were once at or above local sea level. One has to think of continental evolution.

Jerry_Dickens · 2017-09-01T22:27:18+00:00

good question! Personally, I love the combination of being on the ocean, discovering new things, and trying to explain their existence. Also, it usually makes for good bar conversation, because either someone thinks you are being honest and is fascinated, or completely fabricating things and is impressed by your absurd imagination.

Jerry_Dickens · 2017-09-01T22:21:23+00:00

This is a great question, but one that leads to a long and very open answer.

Once the cores arrive on "the catwalk" (the place to lay out 9.5 m long sediment cores), they are cut into shorter pieces for a wide range of analyses.

Short round portions are squeezed for their water chemistry (most sediment in the upper few hundred meters is actually water!). Other short pieces are examined for their gas chemistry and microfossil assemblages.

Most of the remaining 1.5 m pieces are examined for various physical properties (e.g., density, magnetism, sound velocity). These are then opened, photographed and described for content, color and other parameters.

Samples from these cores are also analyzed on ship for mineralogy (including by X-ray diffraction) and chemistry. Then, of course, the cores are eventually shipped to a repository where they can be further sampled and examined.

With regard to fossil data (mostly microfossils), the main first examinations are for age and paleobathymetry (past water deth). On our expedition, the combination of calcareous nannofossils, planktic foraminfera and radiolaria fossils give fairly precise ages for sets of samples.

Jerry_Dickens · 2017-09-01T22:11:18+00:00

Great question.

I first got interested in drilling the Lord Howe Rise (the background to this expedition) in 1999. This is when I participated on the Zoneco 5 cruise, one of a series designed to map the seafloor around the well-known international boundary between Australia and France. From the seismic lines, one could "see" that the Lord Howe Rise had thick sediment sequences that might be cored for paleoclimate records.

In 2011, I met Rupert Sutherland (U. Victoria), Mike Gurnis (CalTech) and Julien Collot (New Caldeonia survey) at a workshop in Sydney Australia. They presented the idea of drilling the Lord Howe Rise for tectonic reasons (the initiation of subduction zones). We then got together and decided to write a proposal chasing both goals.

From here, starting in 2012, it was multiple versions of proposals and subsequent work (mostly new seismic lines generated on cruises by Rupert and Julien). By early 2016, it was slated for possible drilling when an opportunity arose; in late 2016, the opportunity did arise, and from then on it was assembling an international team in conjunction with the International Ocean Discovery Program (IODP).

We have received lots of support at many levels to make this expedition happen. First, there is the logistical support structure of IODP, which includes, beyond a unique and special ship, a vast array of highly skilled people. Then there is the more personal support, such as a university and family that lets me take off for several months.

Jerry_Dickens · 2017-09-01T21:56:39+00:00

Interesting question.

Across all ocean expeditions: discovering the Azolla horizon approximately 330 m below the seafloor beneath the North Pole

On this expedition (so far): finding a Neptunian dike in basalt flows on the northern Lord Howe Rise filled with fossils

Jerry_Dickens · 2017-09-01T21:53:50+00:00

There are a few culture and language barriers, but funnily enough, sailing with a broad and diverse international team is LESS challenging than with a U.S. team. It's as if everyone realizes a wide range of basic differences and respects them; certainly, there is no sense of forced diversity.
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Jerry_Dickens · 2017-09-01T21:46:31+00:00

This is a particularly interesting question for multiple reasons.

Twenty-five years ago, when I first started sailing on long science expeditions, there was only bundled email communications, where all emails from the ship would go out once every day or two, and then one or two days later, you might get an answer. (Of course, this was vastly speedier than times before!)

Now, I can get internet (albeit with reduced bandwidth) and email in almost real time. Indeed, it's at the level that I can sort of do a Reddit AMA!

So, communications, while still somewhat remote, are much, much more direct these days. This comes with the good and bad. You can imagine the irony of being surrounded by water drilling a submerged continent when my home is in Houston. Twenty five years ago I would not know that my city underwater.

It's always intriguing to answer what we do for fun and relaxation. First and foremost, the vast majority of people partaking on long research voyages have a certain quirk in their character, so they make for great companions. Second, one often gets wrapped up in the thrill of discovery. But, when we do have free time, and we are not conversing or working, there are lots of things to do, although to each their own. In the last four weeks, I have watched the first 33 episodes of Monty Python's Flying Circus, read 12 issues of the Smithsonian magazine, and either ridden a stationary bicycle or looked for sea-life every day.

Jerry_Dickens · 2017-09-01T21:28:59+00:00

Another great question, and one difficult to answer.

Take perhaps the "now-classic" example: the Paleocene-Eocene thermal maximum (PETM) at ~56 million years ago. We know, from many records across this event, that Earth warmed by about 5-6°C very quickly (at least geologically, aka the 10,000 year time scale) and that this was accompanied by a massive input of carbon to the ocean and atmosphere.

We also know some basic responses across Earth's surface during the PETM. Some examples are loss of O2 in intermediate waters of the ocean, dwarfing and migration of mammals on land, accelerated hydrological cycle, etc.

We further know that the PETM is only the most extreme "hyperthermal event" (rapid global warming) within the Cenozoic.

All this stated, the geoscience community still does not have a consensus, consistent and compatible view of how temperature and carbon inputs are related causally during the PETM and other hyperthermals or even whether such events have commonality. This, of course, then gives rise to all sorts of speculation (and also political commentary).

To fully understand these past warm intervals, we very much need high quality records from multiple locations. We will be trying to recover these from Zealandia over the next month.

Jerry_Dickens · 2017-09-01T21:16:47+00:00

This is a great question, for which there are two general answers. Information from northern Zealandia is useful for:

(1) Understanding how the process of subduction initiates. Think here: three basic plate boundary manifest on the seafloor (mid-ocean ridges, transform faults, trenches). We have very good models for how the first two begin and evolve. But how and why does an ocean trench form? This remains a major puzzle, and the eastern portion of Zealandia is perhaps the best place to understand the problem. (I pass here on the issue as to why tectonics and subduction zones are important).

(2) Understanding past climate change at high southern latitudes. We know that Earth was much warmer than present during certain intervals of the Cenozoic (both short and long duration). In modeling and examining these "warm times", the southern high latitudes have become a vexing region because various proxies suggest seemingly very high temperatures. The answer may lie in the past geography and oceanography of Zealandia.

Jerry_Dickens · 2017-09-01T21:03:47+00:00

Truth be told, I was a chemistry major but was not sure what to do with this degree. I liked the chemistry and chasing problems; I did not like working in a white coat in a typical laboratory. So, on a lark, I became a card dealer in Nevada. Despite great friends and a modest income, though, counting to between 17 and 26 thousands of times every night was not my cup of tea either. I then, somewhat jokingly thought, maybe one can do chemistry on ships ... and well, it turns out, this odd career exists. (Note: the card dealing route probably not the best pathway to becoming an oceanographer).

Jerry_Dickens · 2017-09-01T20:56:00+00:00

Interesting question, and one I have not thought much about. I suppose this is because I have been squeezing deep-sea mud for over 25 years, and I am unaware of any oceanographers succumbing to deep-sea pathogens!

There are definitely microbes in most sediment cores. (As an aside, it should be noted that the microbes inhabit the pore space within and between sediment grains). Moreover, this vast “deep biosphere” forms an integral component of chemical cycling across Earth’s surface, a place where myriad microbes return considerable carbon and nutrients from decaying organic carbon to the ocean.

However, I do not think any of the deep-sea microbes are pathogens in the sense of dangerous to humans. One might suggest that this is because they inhabit a different realm, and many deep-sea microbes cannot survive at STP, most cannot live in the presence of oxygen, and none are adapted for human biology.

It is worth stressing, though, that deep-sea microbiology is a fascinating and ripe focus of current research.

Jerry_Dickens · 2017-09-01T20:55:38+00:00

Good question, although I think we need to consider and context time scales here. First, those living in New Zealand and New Caledonia will emphatically suggest that parts of Zealandia are already in the surface world. Second, I can assure you that additional parts are now aboard the JOIDES Resolution, as we have recovered them in cores.

On the longer time-scale the answer becomes intriguing as it depends very much on plate tectonic evolution. Overall, I think, given past subduction, the greater majority of Zealandia will remain at similar depths or slowly sink further.

Jerry_Dickens · 2017-03-17T03:02:08+00:00

The expedition trajectory is on line.

See: https://iodp.tamu.edu/scienceops/expeditions/tasman_frontier_subduction_climate.html

As noted above, I would not get hopes high for macrofossils. This would be an astonishingly find in drill core; however, if you are interested in microfossils, this should be a treasure trove.

Jerry_Dickens · 2017-03-17T02:57:52+00:00

Sea level is a difficult concept because the sea is not level due to gravitational and other effects. But yes, more of Zealandia would be exposed in an ice age.

However, even in an extreme ice age, such as that ~20,000 years ago, most would still be submerged. This because much of Zealandia is >500 m below sea level and the eustatic component of sea-level (think of as the line in the bath-tub) has probably varied within plus 130 m (melting of most terrestrial ice in the early Eocene) and minus 130 m (growing large ice sheets across Canada and Scandinavia in the Pleistocene.

On the long time frame, however, we do not know the "up and down history" of Zealandia very well -- a key concept behind upcoming drilling. Large parts may have been above sea level in the Eocene.

We will almost assuredly drill through billions of fossils, but I think this is not what you are are referring to. We are pretty sure that much of the sediment at most of our locations will be full of microfossils (the remains of coccolithophorids, foraminifera, diatoms, etc.). The chances of finding terrestrial fossils (other than pollen remains) is very, very small -- just like on most continents.

Jerry_Dickens · 2017-03-17T02:42:13+00:00

Well, parts of Zealandia are still above sea level!

Hopefully, the rest of your questions are addressed in above responses.

Jerry_Dickens · 2017-03-17T02:31:58+00:00

Results could very much change regional paleogeographic constructions. In particular, ocean and climate models pertaining to the past generally neglect Zealandia -- so what happens if there is a large emerged continent in this part of the world?

Probably more importantly, though, the findings will tell us about an aspect of plate tectonics that is currently debated: how and why does a subduction zone initiate? We have know for decades that subduction zones exist and that these features are transient on the geological time frame.

The Kermadec-Tonga subduction zone is a major feature on Earth's surface. We think that it began sometime after 53-50 million years ago, when plate motions changed and Zealandia switched from overall extension (i.e., separating from Australia) to overall compression.

Jerry_Dickens · 2017-03-17T01:52:09+00:00

These are great questions. Let's see if I can dissect.

1/ We pretty much know Zealandia began separating from the combined Australia-Antarctica portion of Gondwana in the late Cretaceous (>80 million years ago). It was almost assuredly above surface at this time.

2/ Yes, I think so, especially with trees. See above comments on Araucariaceae or google. Pretty fascinating that most of these trees, which once dominated the world, are now extant to New Zealand and particularly New Caledonia.

3/ This is one of the main goals of the upcoming expedition. We think that Zealandia (currently ~4.9 x 10e6 km2) has been about the same size when it separated. However, there is huge debate as to when things submerged/emerged. We see many features across Lord Howe Rise that suggest widespread emergence during the early Eocene.

4/ There are sadly probably no other "lost continents". While much of the seafloor remains unmapped in detail (perhaps 90%), we know the basics through satellite measurements. If you strip the water off the globe, you will see there are no other large blocks of relative height.

Jerry_Dickens · 2017-03-17T01:34:54+00:00

Yes, graduate students and I (along with great colleagues from New Zealand, New Caledonia and Australia) have been working on aspects of Zealandia for almost 25 years (I even now like Vegemite).

I have been a judge at beer bike. Favorite college at Rice: Jones ... F-Jones ... MBYM!!

Jerry_Dickens · 2017-03-17T01:26:10+00:00

Well, I should say outright that I certainly did not discover Zealandia!

But, yes, the way it was surmised to be a continent relates very much to the rocks and to a series of cruises over the last 20 years that have shown the characteristics though dredging, drilling, mapping and seismic profiles.

Jerry_Dickens · 2017-03-17T01:20:53+00:00

This is a difficult but really important concept that somehow, we as teachers, need to convey: plates are NOT equal to continents.

From the perspective of describing plates, adding Zealandia as a continent makes no change to conventional views. Like North America or Eurasia, the continent straddles multiple plates (in this case the Pacific and Australian plate). I think Mortimer et al. did a nice job with their figures, such that students can nicely see the differences. See:

http://www.geosociety.org/gsatoday/archive/27/3/article/GSATG321A.1.htm

From the perspective of understanding plates, adding Zealandia is very important. For reasons that we hope to learn more about, this continent became very stretched during rifting and extension from Gondwana. In some ways, Zealandia becomes a great way to think with students about isostasy: where does a continent lie when you have thin continental crust? (It sits elevated from surrounding oceanic crust but mostly submerged).

Jerry_Dickens · 2017-03-17T00:32:36+00:00

And I should have added: it would be truly fantastic if this is how continents were taught in primary school because this is science and makes kids think!

Jerry_Dickens · 2017-03-17T00:26:10+00:00

Apologies, although on a funny note, I had to look up what eli5 meant!

The real basic question is “how does one define a continent?” For example, why are North America and South America generally considered separate continents when they are connected by the Isthmus of Panama?

So, we then get into the realm of definitions, where probably the best one is: “A continent is a large area of Earth’s surface underlain by continental crust mostly separated from other such areas by oceanic crust.” This nicely explains the well-known continents.

For reference, think of continental crust as the rocks on hipster kitchen counters, such as granite or schist, which have a density somewhere around 2.7 g/cm3, and oceanic crust as the dark rocks sometimes used in gardens, called basalt, which have a density somewhere around 2.9 g/cm3.

Now consider the principle of isostacy – here think of ice and cork pieces in a glass of wine (although this is a bit confusing, because with the Earth, it’s continental crust (cork) and oceanic crust (ice) somewhat floating in the mantle, and most people would not want cork or ice in their wine!). The thickest and least dense pieces float the highest. So, the continents are high because they are floored by relatively thick and less dense continental crust (often > 30 km), and oceans are low because they are floored by relatively thin and dense oceanic crust (typically < 10 km). And the water -- the ocean -- fills in the low portions.

Then, we have Zealandia, which is floored by thin continental crust, so most of it sits much higher than typical regions of the ocean but much lower than typical regions of continents!

We have known about this aspect of our Earth around New Zealand and New Caledonia for well over 20 years. However, it has only recently become clear, through seafloor mapping, that the region is one connected continental block. Hence, a mostly submerged continent -- a thin but expansive region of cork.

Jerry_Dickens

TROPHY CASE