Sunday, February 10, 2019

The winter ocean doing strange things


Hourly water temperature, parsed by year, from the NDBC 46041 buoy off of Washington's coast
I was going through some wave metrics from the Cape Elizabeth buoy and noted this interesting water temperature pattern, and though I would throw up a quick blog about it.  The figure above shows each year's temperature data by day of the year.  The bold red line is this year, 2019.  Water temperature plunged about 2C in a matter of days...a fairly rare thing for the winter when temps tend to be fairly uniform.  

I've highlighted two years in the record when something similar seems to have happened this time of year...in 2014 (the sort of reddish bolded line) and in 2018 (the purplish bold line).

Monthly average water temperature from the Cape Elizabeth buoy (blue line), and the anamoly from the 1999-2008 average (red line).

Its also worth noting that up to that point the ocean was pretty warm.  The figure above shows the anamoly from the monthly average, and we are still in this phase of warm winter ocean water that kicked off in 2015.  In fact at Cape Elizabeth there have been only two warmer Januaries, in 2003 and 2016.


Hourly water temperature, parsed by year, from the Port Angeles tide gauge
 Just out of curiosity I also downloaded the water temp data from the Port Angeles tide gauge...shorter record, same idea.  Same pattern here.  Perhaps its not a coincidence that at about the time that this water temperature plunge started it got really cold here in Port Angeles.

Friday, January 18, 2019

Anatomy of a coastal storm: December 20

December 20, 2018 photo of flooding in the Three Crabs area.  Photo from the Peninsula Daily News


The storm on December 20, 2018 brought some coastal flooding with it...notably in the Three Crabs area on the Dungeness River delta, and locations in Port Townsend.  I'm going to focus this post on the Three Crabs flooding.  Shortly after the event a set of aerial photos shot by John Gussman of Doubleclick Productions began to make the rounds, and a few things caught my attention.  First, this was a still water flood - there was little wave action associated with this event at this location (in contrast to areas exposed to south wind, like in Port Townsend).  As a result, we might be able to learn something interesting about the processes driving this event from tide gauge data.  Second, it was very localized near the mouth of Meadowbrook Creek, which suggested to me the possibility of a river component to the event.  I grabbed those photos, and a few published by the Peninsula Daily News (above) and headed out with an interest in seeing if I could get some flood elevation data.  I had a particular question in mind - was this flood driven entirely by coastal processes, or was there a river component to it?

Debris line left by flooding on December 20, 2018, Three Crabs area on the Dungeness River delta.  Photo collect 18 January 2019
So first, the flood elevation data.  I didn't really need the photos...there were plenty of places where a debris line was still evident, a month after the flood (photo above).  I ended up collecting 52 estimates of the elevation of the flood waters using Peninsula College's ProMark 200.

Location of 52 flood elevation estimates from the Three Crabs area
I'm going to report elevations here in meters relative to NAVD88, to facilitate comparison to tide gauge data collected in Port Angeles (at this location, based on VDatum, NAVD88 is 2.09 m BELOW Mean Higher High Water).  So here are two presentations of the flood elevation data:

Flood elevation estimates based on surveys of debris lines, or water lines from photos, in meters relative to NAVD88, for the December 20, 2018 flood at Three Crabs.
The top panel show the data plotted against longitude, since I was interested in whether there was any elevation variation in the flood that might suggest a fluvial component to the flooding.  There is a bunch of scatter, and its too hard to say.  The points at larger longitudes do seem to be a bit higher in elevation, but that is the opposite that I would expect if Meadowbrook Creek was a source, since Meadowbrook Creek is in the opposite direction.  I'm going to call this inconclusive.

The histogram in the bottom panel provides a sense for the range in the elevations I collected.  The mean of these values is 2.94 m NAVD88, which equates to 0.85 m (2.8 ft) above Mean Higher High Water at this location.  There is a total range in the values of 0.35 m, or just over a foot...with is most likely a reflection of trying to estimate a flood surface elevation from a pile of debris on the side of a road.  

So lets move on to comparing the flood elevations at Three Crabs to tide gauge data collect in Port Angeles.  For this purpose I'm going to compare to the mean flood elevation value from the data I collected, 2.94 meters NAVD88.  Here are the data collected at the Port Angeles tide gauge that day:


The tide gauge in Port Angeles recorded a maximum water level of 2.98 m NAVD88 at 11:36 am that day, driven by the combination of a high tide (predicted to be 2.32 m NAVD88, just above Mean Higher High Water), and a 0.66 m non-tidal residual, or "storm surge".  In this case the "storm surge" was probably driven mostly by low atmospheric pressure.  My conclusion though?  The flooding at Three Crabs very well could have been entirely driven by coastal processes - specifically the combination of a relatively large non-tidal residual co-occurring with a high tide.  

Lets dig a bit further to address two other questions.  First, where does this water level rank in the record collected in Port Angeles dating back to 1975?  Turns out that this was indeed a pretty high water level...but not the highest.  Three other events have driven coastal water level higher in Port Angeles.  The record for that tide gauge was set on 2 January 2003 by an event that was very similar - a high tide co-occurring with a storm surge of 0.66 m or so.  The big difference was in the timing of the tide...the predicted tide on 2 January 2003 was almost 0.10 m higher, and hence the record water level on that date was 3.07 m.  Two other events, one on 31 December 2005 and another on 27 January 1983 also both exceeded this December 20 event, if only barely.  Both of these events were characterized by lower non-tidal residuals, but higher astronomical tides than the event on December 20.  I'm curious about what happened in the Three Crabs area during those events.  

The next question...how bad could it be?  Coastal flooding is a game of chance, with the worst events happening when the astronomical tide is high, and the non-tidal residual is also large.  It gets even worse when we add in winds from the right direction...but lets ignore that here.  So the highest astronomical tide on record for Port Angeles was 2.63 m NAVD88 on 30 December 1986.  Pretty darn impressive astronomical tide!  The maximum non-tidal residual?  That occurred on 1 January 1997 when water level hit 0.9 meters above the predicted water level associated with a notable winter storm.  Fortunately on that day two things happened that kept water level relatively un-exciting (the tide gauge peaked out at a maximum water level of 2.79 meters NAVD88); first, the predicted high tide wasn't that high, and second the peak of the non-tidal residual didn't correspond with the peak of the high tide. 

So how high could it be?  Well what if that highest astronomical tide of 2.63 m NAVD88 corresponded with that maximum non-tidal residual of 0.9 meters?  A peak water level of 3.53 meters, fully 0.55 meters, or almost 2 feet higher than the December 20 event.  Now that would have been unpleasant in the Three Crabs neighborhood.  Fortunately for us the odds of those two things co-occurring are pretty darn low...but we are certain to get higher than we did on December 20...its only a matter of when. 


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