Thursday, December 20, 2018

Sea Level Rise - more than an abstraction


I know that, even as I write this, coastal Washington is getting hammered by some severe storms and coastal flooding.  It sort of feels like I should be focusing on that at the moment.  But the fact of the matter is, I'm on the east coast visiting my parents in Gloucester County, Virginia...and I've got other things on my mind.  I had the chance to meet up with Matt Kirwan, faculty at the Virginia Institute of Marine Science who has largely focused his research on the response of salt marshes to sea level rise. Matt took me down to Guineau, a low marshy peninsula between the York River, Mobjack Bay and Chesapeake Bay proper.  In general this part of the east coast is one of our national hot spots for sea level rise, with historical trends at the nearby Gloucester Point tide gauge approaching 4 mm/yr.

Matt uses historic map's like this 1905 Coast and Geodetic Survey map to find formerly agricultural and forested lands that have been converted to salt marsh
One thrust of Matt's research focuses on measuring the transition of uplands into salt marshes, using both sedimentological approaches (i.e. coring salt marshes) and mapping.  We didn't have a chance to core, but Matt readily pointed out areas of salt marsh that used to be forest land or agricultural lands.  It was also easy to see places where the transition to salt marsh was actively occurring.  In the photo at the top of this post, for example, tree trunks and dead pine trees are readily observable at the interface of this marsh and forest.  As sea level rises, the marsh is moving inland.  Interestingly Matt's work has also suggested in some cases that the leading edge of the marsh may be less response to sea level rise than the landward edge.  In other words the marsh may be much more resilient to sea level rise than previously thought, at least in cases where the marsh is unconstrained by armoring, diking or topography.  

Another view of tree stumps sticking through the marsh surface...evidence of recent habitat transitions.
The signs of sea level change were also evident in the agricultural land we drove past.  Large patches of bare earth in the fields are evidence of high salinity pore water, rendering sections of field unharvestable year after year.  I was astonished to learn that the farmers continue to plant these sections year after year.  The very definition of hope.

Bare spot in a soybean field...too saline for any ag crops to grow.
Finally, I couldn't help but post this photos.  This area was also hit hard in 2003 by Hurricane Isabel and there has been some adaptation as a result of that event:

A trailer raised precariously high on stilts...anything to avoid flood insurance!

Monday, November 26, 2018

Beaten to the punch, part 2: Tsunami Debris

Back in early 2012 Jim Brennan and I published a short technical report through Washington Sea Grant focused on assessing likely debris accumulation scenarios for Washington State associated with "tsunami debris" from the March 2011 Tohoku tsunami.  The report was a response to some dire messages that were promulgated at the time through the media, and even by some ocean circulation experts.  There was some very real anxiety about the impacts to Washington's coast from this load of debris.

Anyway, we used some analysis of previous research and observations, coupled with some liberal hand-waving, to estimate what we considered a likely range of debris loading to Washington's beaches in the first four years after the tsunami, and we came up with an estimate of 1-14 times the background debris loading level.

So that was great, and we got some limited but very nice feedback on the report from some coastal managers on the west coast, and found that it was making its way into management decisions as far afield as B.C.  As the years passed, though, I found myself with a desire to revisit our suggested likely scenario, and compare it to what really happened.  I was involved in a few tiny efforts in the subsequent years, but largely I could never pull it off.  Thankfully, someone else did.  


Earlier this year Cathryn Murray published a paper with Nikolai Maximenko and Sherry Lippiatt examining whether there was a detectable tsunami signal in temporal patterns of marine debris on the west coast, based on monitoring data.  The short answer...there was!  And they used data collect in the Olympic Coast National Marine Sanctuary to estimate that the tsunami debris contributed to a roughly 10-fold increase in debris load to beaches in Washington State...which sits squarely within our 2012 likely estimate.  Very cool!

Fig. 1. Mean yearly debris influx of indicator items from 2003 to 2015 at sites in northern Washington State, USA. Letters denote significantly different groups using Tukeys HSD posthoc comparisons).  From Murray et al., 2018.  
The figure above shows the estimated average rates of loading of a subset of indicator debris items tracked in monitoring efforts over 10+ years at sites in the Olympic Coast National Marine Sanctuary.  This is the source of the estimate that the Tohoku tsunami led to a ~10x increase in debris load.

There is quite a bit more ground covered in this paper, some of it interesting relative to what we assessed back in 2012, and some of it just cool new territory (i.e. the documentation of seasonal spikes in debris loading, which I blogged about back in 2014 in the thick of the tsunami debris period).  Really cool to see this work, and really useful for assessing when and where debris is likely to come ashore in the future associated with any input of debris in the Pacific Ocean.
 

Tuesday, November 20, 2018

Beaten to the punch, again...

A clump of Eudistylia vancouveri, photographed at a location just to the west of the Elwha River delta
Every once in a while over the ten years that I've been diving at Elwha I would see something that struck me as special; an example of an interspecific relationship that I hadn't really anticipated.  

Let me start with a bit of background.  First, let me introduce you to one of my favorite invertebrates, the beautiful Eudistylia vancouveri, or Northern Feather Duster worm.  I'm into these inverts for a few reasons. First, they look like truffula trees, which is just cool.  Next, and perhaps most importantly, they are big, obvious and easy to identify underwater.  When we first started diving the Elwha I always felt a sense of relief counting Eudistylia, since I knew I was going to get it right.  More than anything, perhaps, that explains my appreciation for these worms.  

A complete E. vancouveri individual that we happened to dredge up with a sediment grab.  The scissors are full size.  The tube of this individual measured roughly 1 meter, and the worm almost 0.5 m. 
E. vancouveri is a special tubeworm, notable for how large and stout its tube is.  Diving near Elwha we would commonly observe individual tubes in excess of probably 20 cm...and that was just the bit sticking out of the substrate.  We couldn't really figure out how much additional tube there was below the substrate.  On a few occasions over the years we made futile efforts to dig an individual out of the substrate, hoping to actually measure one.  I dug some big holes underwater, and never was able to get to the end of one of these tubeworms. 

It wasn't until early this year that we collected a complete individual in a sediment grab...purely by accident.  The tube was over 1 meter in length, and the worm itself around 50 cm.  These are impressive worms.  

Looking up at the fronds of bull kelp.  Oh, and there are some fish too.

The other player in this story is bull kelp (Nereocystis leutkeana).  These are a bit better known - they are the fast-growing kelp that, under some circumstances, are able to grow all the way to the surface, where you can easily observe their buoyant bulb and fronds from a boat or kayak.  These bull kelp require (or so we told ourselves) hard substrate to attach to - ideally bedrock.  They can grow on smaller boulders and gravels, but as they grow and the cross-sectional area of their stipe and fronds increases, it becomes more and more likely that they will mobilize these coarse grains  After that, these kelps are on the move...and frequently won't survive the ordeal.

A common site near Elwha - Nereocystis attached to coarse clasts.  As the kelp grows it mobilizes the clasts and the algae no longer can stay in one spot.  This typically ends poorly.
So around Elwha it always struck me that one of the challenges for Nereocystis, and maybe even a limiting factor for its distribution, was finding available stable substrate. Every now and again, though, we would see enterprising Nereocystis taking advantage of the stability of E. vancouveri to find a place to hold in relatively fine substrates.

Nereocystis attached to and growing on Eudistylia.  This photo was shot near here.  This is a pretty energetic area - high currents and decent surge - and no bedrock.  Its likely very hard for Nereocystis to find stable substrate to hold on to in this area.  
This all came up for me after reading this article in the Hakai Institute's excellent magazine.  There is a lot to like about this - I love the story here about the serendipity of this discovery, and the convergence of an observation with a "prepared mind".  In this case Matthew Bracken was prepared enough to know how special the relationship that he was seeing really was, and to document it.   I wasn't - I thought it was cool, but wasn't prepared enough to know just how cool it was.  So, again; beaten to the punch.  Maybe there still is a chance though...is this the first documentation of this relationship with Nereocystis?  




Monday, November 12, 2018

Great fields of sand

Looking south towards the Olympics from the San Juan Channel
Man, its been too long....almost three months since my last blog post.  Too much going on.  I still have a fourth edition of the sea level rise posts I started back in August in mind, but I'm going to back-burner that in favor of a shorter and easier post.  I'm back at Friday Harbor Labs, once more teaching the Marine Sedimentary Processes research apprenticeship.

Last week our class had one day of time on the R/V Centennial that we have traditionally used to make a long one-day cruise to Elwha.  But we decided instead to stay local, partner up with other classes at Friday Harbor, and make a trip out to the sand field in the San Juan channel.  We had two over-all goals.  First, many of the students had projects focused on investigating the use of this sand field by Pacific Sand Lance...and much of our time was spent pulling sand samples from the field, and sorting the PSL out of those sand grabs.  Next, we wanted to sample around the sand field to get a sense for the grain sizes immediately adjacent to it.  How distinct was the boundary of the field?

The name of the game is plucking as much sand as possible off the bottom using the biggest grab available

Sorting through a sample of sand

Pacific Sand Lance, and coarse sand
So first off, the PSL utilization of this sand field is unbelievable.  We took a total of 10 grabs of sand from the field, with the grab bringing maybe 5 gallons of sand to the surface at a go.  The average number of fish in each of those grabs was probably about 15...and the max?  An incredible 50 fish in one grab.

Pacific San Lance emerging out of a sample of sand
Interestingly enough, while the abundance of PSL in the sand field is pretty high, the sand field has pretty low diversity of invertebrates.  Just a few were pulled up.

2 of these shellfish came up, from 10 grabs.  Juvenile Clinocardium?

One sample included this beautiful worm.  Flatworm I think?

And out of 10 grabs, one amphipod.  

Our samples away from the sand field were, perhaps unsurprisingly, pretty coarse.  The currents in the channel are intense, which presumably makes this area unsuitable for the deposition of most fine sediment.  But it begs the question...how is the sand field itself maintained?  How does it persist?  These samples outside of the sand field were also notable for their relatively high invertebrate diversity.

A characteristically coarse grab sample from the San Juan Channel, outside of the sand field
We pulled up a good number of these beautiful brachiopods...its been a good long while since I've seen one of these.  I think maybe Hemithiris?  There is a lot of interest in these, not least because they are so prevalent in the fossil record.  


High chiton abundance, but we dredged up only tiny specimens like this one

A couple of these came up...juvenile Cancer oregonensis I think?

A great wealth of Podedesmus at these sites...shown here with a nice encrusting bryozoan

The only scallop we pulled up, and I'm not totally sure, but maybe a rock scallop (Hinnites) just prior to cementing itself in place (?), with maybe a boring sponge (Cliona??)



Thursday, August 30, 2018

Sea Level Rise: Why We Care, Part 3


In the last post (Part 2), I started to connect climate change to sea level, focusing on how very small increases in ocean temperature can lead to meaningful changes in sea level via expansion of water.  In this post, Part 3, I want to draw a connection between climate change and the other big process that drives most of the climate driven sea level rise projected for the coming decades:  The addition of new water to the ocean basins.

This component of sea level rise is similarly straight-forward (like the thermosteric effect) and driven by processes that we tend to interact with on a day-to-day basis:  If you warm up ice, it melts.  In this particular case we are particularly concerned with large masses of ice grounded on land, things like glaciers perched on mountains or at the edges of ice sheets:

Global map of glaciers (in blue) from the Randolph Glacier Inventory.  See https://earthobservatory.nasa.gov/images/83918
As well as ice sheets (in white in the map above) in Greenland and Antarctica.  As these masses of ice melt, and since they are perched on land masses, when they melt the meltwater flows into the ocean basins, effectively filling them.  Details about how these big masses of ice melt (and also how quickly) are one of the primary sources of uncertainty in sea level rise projections, and compound uncertainties just about climate change (i.e. even if we knew exactly how certain emissions scenarios would influence future temperature, we still wouldn't know exactly how much melt that change in temperature in either the air or water would cause).

What we do know, though, is that these big masses of ice ARE currently melting in a net, long-term sense.  The GRACE satellite mission launched in 2002, and provides near-continuous monitoring of the gravitational forces exerted by the mass of the Earth.  Here is the thing - as these big masses of ice melt, they lose mass.  Therefore their gravitational attraction changes, which can be measured by this satellite mission.  As a consequence you get data like this for Greenland:

Courtesy of NASA: https://svs.gsfc.nasa.gov/30879

or this one for Antarctica:

Thank you NASA!  https://svs.gsfc.nasa.gov/30880

And both of these allows us to assess how much mass is lost or gained from these big masses of ice (and also where it is lost from...which is also interesting and tells a story).  By way of reference, melting roughly 362 Gt of ice leads to 1 mm of global average sea level rise.  Lets play a quick numbers game:  If these masses of ice continue to melt at the same rate as they have since 2002, contributing something like 1.5 to 2 mm/yr to global average sea level...well that will be hard but probably manageable.   That leads us to something like 1/2 a foot of sea level rise by 2100 (from the ice alone...).  The concern though, is that these ice sheets are only just getting started (and there is some evidence for that), and that the possible contributions from Antarctica alone by 2100 may measured in multiple feet.

Its worth noting that sea ice, which is frequently covered as a climate change indicator, does NOT play a direct role in driving long-term sea level change (which isn't technically totally true...but the influence is very small).  It is frozen in the ocean, and therefore displaces seawater.  However, sea ice likely plays a role in buttressing glaciers and ice sheets, slowing them down a bit as they flow into the ocean

Wednesday, August 29, 2018

Sea Level Rise: Why We Care, Part 2


In my last post I attempted to lay the groundwork and evidence that I look to that supports the concept of anthropogenic climate change.  In this post I want to connect climate change to sea level.  That connection, in my mind, is pretty straight-forward and rests on some pretty familiar processes.  

First, though, lets review.  The fundamental idea behind climate change is that as we add greenhouse gases to the atmosphere, especially those that are long-lived (like carbon dioxide), we increase their concentration in the atmosphere.  Those gases then start doing what they are supposed to do...they begin trapping extra heat in the atmosphere.  To be clear, there is a good bit of very fair debate about what is called "sensitivity", that gets at how much warming we should expect from a given increase in the concentration of greenhouse gases.  These are critical questions to address, and I'm no expert on the details (though there are a number of excellent summaries available).  Rather I tend to trust the train of logic that I've laid out thus far...we know that gases like carbon dioxide are greenhouse gases, we know that we are actively transferring carbon from the ground into the atmosphere, and as such its reasonable to expect that this transfer is likely to influence global climate, and lead to warming.  There is also compelling analysis that suggests that we can actually observe the earth system absorbing extra heat energy.  

So lets, finally, get in to the connection to sea level.  Extra heat energy retained in the global system should lead to warming, and so we would expect to find that warming in the atmosphere, and also in the ocean.  This warming is linked to two processes that are the most important processes for driving sea level rise.  Lets walk through each in turn.

First, as ocean water warms, it expands (known as the "thermosteric effect"), and it really doesn't take much of an increase in temperature to drive meaningful sea level rise.  It is easy to see that, because the oceans are deep, the very small expansion of water expected with that small increase in temperature leads to meaningful changes in sea level.  Lets walk through this example that I use with my introductory Oceanography classes.  First, we are going to visualize an imaginary ocean is 1 meter on each side, but is 4000 m deep (the average depth, roughly, of the global ocean) - this just makes our math easier.  Our ocean sits in a basin.  Here is my hand-drawn rendition of this ocean:

We are also going to imagine that this ocean has a temperature of 4C (roughly the average temperature of the global ocean), and a salinity of 35 psu (roughly the average salinity of the global ocean).  We can then use a density calculator to estimate the density of the water in our ocean.  I come up with 1027.786 kg/cubic meter.  We need this density, because what I want to do now is calculate the total mass of water in our ocean, which we can do if we know the density and the volume of our ocean (density has a very simple definition and equation).  We've got both, and can easily come up with the mass:  4,111,144 kg.  Our ocean is heavy. 

Okay, now lets warm our ocean up by just 1C.  This isn't much, but is within the range of end of century possibilities for the global ocean.  In fact, measurements suggest that the surface of the ocean has already warmed up by around 1C since the beginning of the 20th century, some of which is likely due to anthropogenic climate change:



Its worth noting here that the ocean is FAR HARDER to warm up then the atmosphere, both because its mass is so large, and also because water has a much higher heat capacity then air.  So here is our warmer ocean:

You will note that with the temperature increase, the density of our water has gone down a bit...a very small bit...but a little.  We've expanded our water ever so slightly, so a unit volume of it weighs just a tiny bit less.  We also haven't added or removed any water from our ocean, so we have not changed the mass...and we've got the new density, so we can solve for the new volume of water again using our very simple density equation.  I come up with 4000.432 cubic meters.  Our ocean has a new volume.  Now, since our ocean is only 1 meter on a side its easy to figure out that our expanded ocean must go up by 0.43 meters due to this very small increase in temperature.  0.43 meters is roughly a foot and a half...not much relative to the depth of the ocean, but relevant when we start to think about all of the development and value that we've put right at the edge of the ocean.  By increasing the ocean's temperature just a bit, we've suddenly started to bring the ocean's into contact with a lot of value - homes, infrastructure, habitats, roads, etc. - that we never intended to be in contact with the ocean.  Its also worth noting that a foot and a half of thermosteric sea level rise is roughly consistent with end of century projections.

So that is the first big component or process connecting climate change to sea level rise.  Remember in this example we kept the mass of the ocean the same as we warmed it up.  There is another big component driving sea level projections though, one that adds new water to the ocean basins.  We will get to that one next, in Part 3.

Tuesday, August 28, 2018

Sea Level Rise: Why We Care, Part 1



Just a few weeks ago we published an updated sea level assessment for Washington State, for which I was the lead author.  We anticipated a small splash when we released our assessment, and indeed were covered in a variety of print, radio and TV outlets:

Along with that coverage came a smattering of emails from people around the state, most of them just from individuals, and some appreciative, some dismissive, and some thoughtful.  One stuck out for me for its honest skepticism:

"With all due respect, how do we know that this is not fake news? I think a lot of us out here are very skeptical of this kind of reporting and these studies because we don't understand what it's based on and bias."

We intentionally didn't dive too deeply in our report into the basis for the concept of climate-driven sea level rise - that wasn't the purpose of the document.  However, I figured I would at least take a crack at starting to address the question implicit in the comment above on this blog.  I frame that question as follows:  "Why is sea level rise a thing?  We have enough stuff to worry about, so why should I care?"  The full answer to this question is well beyond the scope of this blog, and my expertise.  There are probably hundreds, if not thousands, of papers that, together over decades, put together the full story of the connections between greenhouse gases and changes in sea level, but the story that I'm going to tell in multiple parts is my simple way of thinking about that question.

It starts here, with the concept of climate change driven by greenhouse gases.  As many have pointed out, from a geologic standpoint this isn't a new thing.  Greenhouse gases have apparently changed the Earth's climate on multiple occasions in the planet's history.  The primary culprit in most (or all??) of those cases, though, wasn't human emissions, but rather large volcanic flows.  Starting a few centuries ago, though, humans started transferring buried carbon from underground, back into the atmosphere, via coal mining, and then the extraction of oil and natural gas.

There were a few observers in the late 1800's and early 1900's that put together the pieces.  The key insights about the heat-absorbing properties of carbon dioxide, water vapor and other greenhouse gases were made by John Tyndall and reported in 1859 (the story of which is wonderfully recounted here).  These observations of the properties of atmospheric gases provided evidence to support hypotheses about a "greenhouse effect" on Earth originally posed in the 1820's by Jean Baptiste Joseph Fourier.  It didn't take too long for someone to make the connection between the properties of gases that John Tyndall described, and the mining of coal that started in earnest in the 1800's...and indeed in 1896 Svante Arrhenius published a paper describing how changes in carbon dioxide concentration in the atmosphere should lead to changes in temperature on the ground.

To me, these early insights about gases and the global system lay the groundwork for two fundamental ideas that, based on their insights, I trust:

1)  The idea of climate change - that greenhouse gases can control, or change, the Earth's climate

2)  That humans are capable of adding those greenhouse gases to the atmosphere via extracting fossil fuels from the ground, and transferring the carbon they hold to the atmosphere.  Its not just volcanoes that can do that.  

From there, rather simply put, the rest is details.  How exactly does carbon move through the Earth system after it is added?  How long does it take for geologic processes to remove carbon?  How much does the ocean absorb?  How much does adding a certain amount of different greenhouse gases to the atmosphere change temperature?  Where and why are there differences around the globe?  How much of warming that we observe is due to greenhouse gas emissions, versus "natural variability"?  The list goes on and on.

There are highlights along the way.  In 1958 Charles David Keeling began to focus on monitoring carbon dioxide in the atmosphere, and his efforts are on-going to the present day:


and clearly demonstrate a trend in carbon dioxide concentration in the atmosphere.  

Also in the 1950's, the development of micro-processors started to lead to rapid advances in the ability to model processes related to Earth's climate, and in the 1990's led to the development of global climate models, which are now widely used in efforts to translate scenarios of future emissions changes into estimates of future greenhouse gas concentration, temperature change, and a slew of other climate impacts.  Climate models are complicated, imperfect and most definitely aren't my expertise, so I find these sorts of layman descriptions helpful:



Climate models, there use, short-comings and applications are probably the key source of confusion about climate change, and perhaps rightly so.

The 1990's and early 2000's marked the emergence of climate assessments - efforts to review, sort, rank and summarize scientific developments about climate change and its associated impacts.  Early on these processes were international, and more recently national, regional and local, and also associated with mitigation or adaptation planning processes.  

I will stop there for now...and we haven't even yet touched sea level.  That is coming up next.  My key take-away from this Part 1, though, is that there is a real basis for the concept of climate driven forced by humans.  There certainly is real and honest debate about the details, but we will start Part 2 with that concept.