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.

Tuesday, August 7, 2018

The Rock Pile

Extirpation of Pycnopodia?  Not a thing at this site.  Pycnopodia were plentiful and there were more than a few larger specimens.
I had the chance to team up with the Elwha Interagency dive team again this year, for a truncated version of the Elwha dive surveys that we've been conducting since 2008.  With just 5 diving days (Rather than 15 as in previous years) we turned our attention towards surveying priority sites from amongst our set of ~20 locations that we've been able to visit in previous years.  

However, as can often be the case, we also have to contend with losing dive time to bad weather.  We did pretty well this year, but lost our last half a day due to wind chop and swell.  Instead, we used that time to visit a site in Port Angeles Harbor called the "Rock Pile" that requires special access authorization from the USCG.  It is a pretty cool, and great for fish...



Cabezon

Once more...Pycnopodia!

Dermasterias imbricate...a nice big one.
Copper Rockfish (and another Pycnopodia) in the rocks
Notably, we also spotted a GPO, our first since 2016:

Monday, June 25, 2018

A land made of sand



Looking north along the shoreline towards the Big Sable lighthouse on the eastern shore of Lake Michigan
A little family vacation this year means a trip to Michigan, and a few days spent in my wife's childhood summertime haunts near Ludington, Michigan.  We've spent most of our time in Ludington State Park, which sits on the incredible Big Sable Point.  As far as I can tell the whole landscape here is basically a big pile of sand blown out of Lake Michigan, which makes for a prime opportunity to check out various sand transport processes at play, and their resulting landforms.  So first off, a reminder (mostly for my benefit) that the vast body of water that we've been gazing out on to our west:


is, indeed fresh:
but the process scales here ARE extraordinary, and very ocean-like in many ways.  There are actually tides at play, though they are small.  But there are larger water level variations (of around 4 feet based on the last 50 years of record) driven by an interaction between precipitation, evaporation, outflow, and seiches (which seem to be driving little 1 inch sub-hourly variations in water level over the last day).  Waves are clearly a force here - I geeked out for a bit on these little lines on the shoreline, each deposited by an individual wave scouring sand from the beach face and pushing it landward.  


at the same time there are signs of erosion everywhere, not only indicated by the seawall built to protect the Big Sable lighthouse (photo at top), but also by the erosional scarp along most of the lake edge:

But wind is clearly the main player here.  My guess is that periods of low lake level lead to drying of shoreline sand, and rapid aeolian transport.  The resulting dunes are impressive:


and clearly mobile (as indicated by the complex stratigraphy exposed on this dune):


Dune grass (an Ammophila species, though I'm not sure which one - but may be native here?) is widespread (and so impressive in its ability to survive in this environment):


and probably contributes in some way to dune stability.  I was struck, though, looking at Google Earth Engine's timelapse, at how LITTLE obvious dune migration there is over the last 30 years:


I have no idea how much dune grass contributes to that stability.  But, as in a lot of locations Ammophila DOES contribute to the creation of a distinctive dune morphology.  Here is a beautiful view looking down the trough between the primary foredune (to the left in the field of view) and the secondary dune (to the right):



Behind the secondary dunes is a wonderland.  Currently the lake is pretty high, and there has been recent rain, so the landscape is peppered with these beautiful little ponds:


Interestingly, in this particular location the ridges between these ponds were actually paved with these gravel cobble lag deposits, which were beautiful...but also a bit odd to try to figure out how they ended up here.  Anyone want to take a stab?







Tuesday, June 12, 2018

Elwha Update

The date is approaching for our annual topo/bathy survey of the Elwha delta and so I figured it would be the right time for a bit of a year in review from my own monthly survey work.  Here are the story-lines as I see them:


1)  The transition of the old estuary.  This isn't new by any stretch, and has been well documented by a variety of investigators (i.e. see this and this).  But I've been struck by the visual transition.  Above, for example, is a shot from this morning (looking south from here) of what used to be a pretty sizable estuarine lagoon.  Here is that same view in February 2013 (this photo was shot from the other side of the picnic table here):




That formally open estuarine lagoon has been rapidly filled with fine sediment, colonized by cattails and other vegetation, and seems well on its way towards becoming a marshy forest.  

2)  The terrestrialization (is that a word?) of the former intertidal near the river mouth, in the zone where the river dumped most of its sediment, this view from 2011 (shot here):

2 August 2011
now looks like this:


That IS the same location.  

3)  And continuing with the theme of transitions, the nourishment of the beach to the east of the floodplain, under the bluffs.  Here is a photo taken today here:



and from the same location back in September 2013:


I've got some profiles and other data from this location all the way at the bottom of this post.


4)  Lets look at some beach profile data, most of it collected over the last year.  I shot the photo below today, of a band of buried wood waste (mulch, small sticks, etc) eroding from the intertidal beach right about here:

This area has been quite erosional since 2015 (see profiles for the last year below), and I'm assuming that this material is made up of deposits from one of the lagoons that formed behind the seaward bar during the peak of dam removal.



Just to the west, closer to the river mouth, the seaward bar has also been quite erosional, but over the last two months it looks as if a new little lower intertidal bar formed, and then welded to the beach face:



As you move away from the river mouth, both west and east, there has been quite a bit of stability to the beach.  Here, for example, are profiles from about here to the west of the river mouth:


and this site to the east, that just a few years ago was eroding at average rates of more than 5 meters/yr:



Over the last year the shoreline position at both of these locations has fluctuated within a window just a few meters wide.

The very far eastern side of the floodplain also seems to be on a trajectory of change.  Here, for example, are beach profiles and shoreline position time-series date back to 2011 from this site:



This area is quite interesting, as it is east and downdrift of a major rip-rap removal and beach restoration project that happened back in August 2016 (see this and this), and sits right next to a subsequent house relocation and armor removal project that happened in August of 2017.  I think that you can see the August 2016 project in the shoreline position time-series above, manifested as that first and tallest spike centered on 2017.  The winter 2018 spike in shoreline position is also interesting, and may be attributable to that second project...or maybe we are seeing some sort of seasonal transport signal at play.  I'm intrigued though, that the section has continued to erode after those projects wrapped up.

By contrast, the overall combination of massive supply of sediment from the dam removal, coupled with the removal of rip-rap in August 2016 that was blocking transport to the east, seems to have led to a shift in the shoreline under the bluffs (here).  Here are the profiles and shoreline position time-series dating back to 2011


and of course the photos set above (comparing today to September 2013) is from this same location. This section of shoreline really took off in the summer of 2016, and while it seems to have the same possible seasonal (maybe?) pattern going on (spring/summer erosion?) the overall trend has been towards nourishment and beach accretion.