Yes, good afternoon. As Johanna said, I want to still talk a little bit about the North Sea,
and I went in 2004 actually to Canada, so it's quite a while ago.
But about a third of the work is still in the North Sea, and part of the reason is that this is basically,
as Johanna said, a long-term collaboration, and this goes now for longer than 10 years,
and there's a very nice expertise and also database, a valuable point which we have built our work.
And I want to present some ideas of this work today, and more specifically,
I want to talk about the carbon and the CO2 or pH regulation in the southern part of the North Sea,
so in a very well-ventilated area, which is sometimes a little bit more difficult to assess in stratified waters,
but I will speak a bit about stratified waters initially also to set up the differences.
So I should start with the final slide, basically. This is a long group effort,
and Johanna obviously has played a strong role, despite the fact that I don't show any model picture today.
There's a number of colleagues and also students' work involved,
and more recently, and you will see a lot of his work at the end of the talk,
he did his PhD defense a couple of weeks ago on the topic I will speak about,
but there's also many other people, and also the groups from Holland and Belgium,
and also from Germany are involved, and you can see this easily from the data sets
and from the work that has nothing to do with a single-person work,
so it's really a group effort, and I'm in a fortunate situation to talk about this a little bit.
Can everybody hear him?
I can try, I can also try to try this one.
Yeah, okay.
As an outline, I want to discuss a couple of ideas on why we look at the carbon cycle
in coastal or shallow waters or marginal seas, and what might be the difference to the open ocean situation,
and I will come back to this at the very end again when I talk about eutrophication and ocean acidification,
and you will see in particular in the last section the big differences between the shallow and the deep ocean waters,
and I will start then with a little repetition or introduction of the CO2 system
in the surface waters of the North Sea on the seasonal scale,
and then will look more in the role of the sediments or shallow sediments
on regulating the CO2 system in surface waters and also the pH in surface waters.
One of the drivers of this research, and you have seen this probably a lot,
is the monolure curve, and the topic of ocean acidification has added a little bit a new trigger or spin to the work,
and this plot shows you the rise of the atmospheric CO2 concentration as recorded in Hawaii,
and it started from about 310 or so in 1960 to more than 400 ppm nowadays,
so the curve stops a little early, but we are now somewhere here,
and if you go to Hawaii, which is an open ocean situation, there is not much influence of land available,
so the open ocean waters basically have no choice in following the atmospheric trend,
following Henry's law, and it absorbs a part of the CO2,
and thus there is the surface ocean PCU2, which is a blue vine,
in the end follows the rise of the atmospheric CO2 concentrations.
Broadly speaking, you can see very nicely that the atmospheric PCU2 and the ocean PCU2 track each other nicely in open ocean waters,
and the reason is simply that there is no choice and there is also no other influences from land
and from the sediments which would affect the relationship between those two.
And since carbon dioxide is a weak acid, basically the ocean surface water pH also adopts this trend,
and there is a decreasing ocean pH observed also in the survival station,
and this is the measurements, or high-quality measurements of the C2 system started in the mid-nineties,
so this is why the two ocean curves start about 93 or so,
and since then you can see basically the surface water PCU2 following the atmospheric concentration
and the pH doing the same thing, but if you add the weak acid carbon dioxide, the pH goes down.
So this is what I have written as a recollection here at the bottom, so if you add carbon dioxide to the water,
you create basically unstable carbonic acid and this then dissociates and releases in the first dissociation step in proton
and also the second dissociation step.
And then some people look more from the reaction, what you do if you add C2 to the water,
in the end the carbon dioxide reacts with the carbonate ion and then forms bicarbonate,
and this is a classical geology, a veterinary action.
I'm not really so much a friend of this expression, but what you do see is if you add C2,
basically you decrease the carbonate concentration,
and this is kind of the second problem of ocean acidification,
that you lower the carbon concentration, then the calcifying organisms run into trouble.
But this is not so much what I will be talking about here.
The main part of the talk is basically about the DRC and alkalinity,
which are the two major controls of the CO2 system and also of the pH.
And I will speak in the next minutes about processes changing the DRC
and processes changing the alkalinity and the DRC together.
And this is basically the particular situation in shallow oceans,
that the alkalinity change from the metabolic or biological perspective is basically possible in the cell of the sediments,
but in deep oceans this is not observed,
because the deep ocean sediments are fully disconnected from the surface waters,
and in well mixed surface waters of the shallow oceans,
the sediments basically are in contact with the atmosphere,
only separated to one mixed water layer.
And this is basically summarized in this figure here,
that if you start on the left-hand side, which is not on the plot in the open ocean Hawaii situation,
this would be somewhere here.
The only effect basically where the open ocean responds in terms of CO2 to a trigger
is the atmospheric surface water interaction.
And this we saw on the Hawaii slide,
that if you ignore everything which is shown on this part of the plot,
the only trigger basically is the atmosphere and biology,
and then the reflection is that the atmospheric PCU2 and the surface water PCU2 follow each other.
But if you move in the shallow water area,
you add the bending compartment,
and you bring this much closer to the surface waters and to the atmosphere,
you add the groundwater discharge or the shelf edge or the water sea area,
and in terms of the torque I will bring in the next couple of minutes,
you have the river as an influencing factor,
which is a freshwater signal in the end,
and also you have a land-based impacts,
which can come through the atmosphere or directly through rivers,
and the nitrogen cycle, for example,
is severely impacted by the land-based input,
and the nitrate input to the surface ocean comes about a third or so,
or substantially via the atmosphere,
but also very substantially via the rivers.
And what I will look at in the next minutes is really about the ramification
of these processes in regulating the surface layer,
PCU2 and PH,
and then we will see that the surface ocean often does not track the atmosphere,
and I try to explain why this can be the case in specific situations.
There's also another factor which affects the carbon cycling in coastal areas,
and this is ourselves,
and there's a table shown here, for example,
these are ten of the ten megacities in the world,
so the ten largest cities, and they are all between 30 million people,
and the yellow ones, the seven ones,
are actually one which are directly in the coast,
so there's enormous influence of the human activities on the coastal seas,
and another number which you often can find in the Gattuso paper,
or in others, and this varies a little bit,
but about 80% of the global population are actually living within 100 km of the coastline,
and the effects of this human presence and activities,
of course, are very, very evident,
and also in the very last part of this talk I will come back to this again,
and this brings us to the North Sea,
and this has been identified for a long term as a very,
let's say, or they call it problematic area,
but in neutral terms as a heavily influenced area,
this nutrient runoff and also ship traffic and tourism,
and nowadays also wind energy production,
so there's a very strong influence of human beings
to the coastal system carbon cycle,
which goes far beyond what's only written in this slide here.
So what we started, and Johannes mentioned this briefly,
we started the carbon cycle observations in the end in 2001
and did about 90 stations map on the North Sea,
we sampled all the carbonate and nutrient system parameters
in four seasons consecutively,
and then tried to maintain the time series,
this three follow-up cruises in 2005, 8 and 2011,
the most recent one, so that we can slowly track the system over time,
and in 2011 we actually had a nice thing that we could bring together,
sedimentary work and water column work,
which is from the logistics, not always the easiest thing on the ship,
because the water column people usually want to have a very clean environment,
and this is not possible if you have sediment,
but in the end this was an attempt,
which worked very nicely,
and I will show a couple of results from this cruise in the next minutes.
The important thought which is behind this is
what process regulates the PC2 and the pH,
and as long as oxygen is present,
the situation is fairly simple,
so the carbon is usually affected by primary production of the spring bloom,
so the PC2 goes down and the AC goes down and alkalinity is nearly unaffected,
and as a consequence you have in spring the PC2 goes down
and the pH goes up because you remove the weak acid,
and then you have the respiration under oxy-conditions,
which is usually the autumn situation, you have the reverse,
so CO2 is released back to the atmosphere,
still alkalinity is not affected,
and then in the end the PC2 goes up again and the pH drops
because it releases CO2 as the weak acid.
Systems become more complicated,
and this is where the shadow sediments play an important role
if you add anaerobic processes,
because then the DSC to alkalinity ratio changes
and you release usually both DSC and alkalinity,
and the ratios are not very predictable,
and the similar unpredictable is the response of the PC2 and the pH,
so the problematic area is really the anaerobic respiration,
if you start bringing together alkalinity generating processes
and DSC affecting processes,
and as long as you have oxygen present the situation is comparatively simple
because it's only the DSC or the CO2 reacts,
and you will see this through the later part of the talk,
and this is basically the most important background concept,
because if you start coupling the DSC and alkalinity generating processes,
you get a very different and very unpredictable picture
if you want to speak about surface CO2 fluxes and pH.
The concept which you can think about what happens in the deep
and in the shallow ocean is basically shown in this little sketch,
so this is again a sketch from the North Sea,
and you can think about the separation line between a stratified and unstratified area.
If you have a mixed water column permanently,
basically you have your CO2 concentration as a background,
and then your primer production in the end takes up the carbon dioxide
and then the respiration from the dying or sinking algae
basically releases the CO2 back in the same compartment,
so what you have in essence is a very little or minor
or non-existing net effect on the CO2 Fc fluxes on the pH,
and you would assume that the CO2 and pH basically remains fairly constant
in the water column of a permanently mixed area,
and this is what you also can see on the next slide.
And then in the corner, if you add a deeper layer to the ocean,
this comes very close to the open ocean situation,
you have basically your production uptake of carbon dioxide by algae,
and then the particulate matter sinks and the respiration basically occurs in the deeper layer,
and in this you basically separate the production and the respiration in space
and sometimes also in time.
And then if you add an exchange possibility,
you can also move this deep water CO2 out of the North Sea,
and then eventually the CO2 which went through the metabolic system and sinking
and export will be replenished from the atmosphere,
and this is more or less similar to an open ocean situation.
And you can see this very nicely if you look at the profile of DSC in a stratified area,
so if you start with the winter situation,
this is basically the line which is straight and homogeneously mixed down to the bottom,
and then you start with the spring bloom,
or photosynthesis basically it starts absorbing CO2 in the surface water,
so the concentration decrease, the particles sink,
and you can see an increase in the same time over spring and summer of CO2 in the deep water,
and this is basically the respiration followed by the sinking.
And then if you go out and basically the mixing of the water column
vanishes the separation and you get again your winter situation.
You can see this very nicely, and I wanted to have this slide in,
so I will show it, this is the carbon isotope distribution.
In the end, the carbon isotopic distribution is not so much of a mass balance approach,
it's more an approach to color code your molecules
or you trace your carbon molecules where they come from
or which process has altered them,
and the carbon isotope is basically two stable isotopes, carbon-12 and carbon-13,
about a percent or so is the carbon-13,
and what biology does, it can take a little bit easier up the lighter isotope
because it takes less energy, so if you have a productive situation,
the heavy isotope is left behind in the surface water,
and this is basically the mirror image of what you see here below,
above basically the photosynthetic energy take up the CO2,
but they only take up the light CO2 because the heavier they don't like,
and what you see is basically enrichment in the summer situation
of the CO2 isotopic signature toward heavier values,
and then what you also see, if the particles sink,
they carry the lighter isotope energy down,
and then the respiration which you see here in the bottom part
releases the lighter isotope back to the water column,
and you can see that the isotopic signature of the CO2
is shifted toward lighter values or more negative values,
which creates basically the separation in the heavier isotope CO2 in the surface
and the lighter isotope CO2 in the subsurface,
and what you would expect from a layer where there's no separation,
basically where the production respiration of organic matter occurs in the same box,
in the end the net effect is zero,
and you shouldn't see any strong signal in the carbon isotope signature
because it will be vanished as soon as it's produced
by the parallel and the same spot occurring respiration production.
Indeed, this is actually what we see.
You can see a nicely mixed carbon isotopic signature,
and without wanting to go too detailed into this,
you can also see that it's somehow in the middle between the two processes.
So you can nicely see that the production,
which is basically this part spring to summer,
basically leaves the heavier isotope behind relative to this red line,
and the respiration basically releases more CO2 in the deep water, which is lighter,
so the signal will be lighter than the average or mean signal in the surface water.
If you now take this step, which points in the end to the problem with the shallow waters,
you can plot the surface water data PCU2,
which is the difference between the atmosphere and the ocean,
and this is our observation.
So if you start with the winter situation,
basically the biology should be in winter mode, so not active,
and the wind will have equilibrated most of the waters,
and so you can nicely see that the partial pressure differences
in the wind is near zero or equilibrated
because it's a biologically inactive system,
and the water column had enough time and enough wind to equilibrate.
And then basically you see what you can predict from the previous slide.
If the biological production kicks in, it absorbs CO2 very strongly,
so this is basically the transition from this line
towards the left-hand side to lower CO2 concentration.
So the whole system basically is under-saturated
because of the very, very active production and CO2 uptake,
and then if the system continues in summer,
you start seeing the difference between the shallow and the deep ocean.
In the deep ocean, basically the separation of the water column
into the bottom and upper part clearly maintains under-saturation
because the respiration of the particle happens in the subsurface layer,
which you don't see here, but in the shallow waters,
which is non-stratified, basically the respiration
and the temperature difference raise the PCU2,
and you get in summer a very warm, rising CO2 signal
because there's no escape route.
And this is, in the end, what I try to indicate here,
that the process basically, in the end, you have a net zero signal from biology,
and what you see is eventually a temperature-driven CO2 characteristic,
the fact that this is a very active area,
but the next net signal is basically zero because it's all in one box,
and this is what you can see here,
so it's a temperature, or apparently temperature-driven warming,
compared to the strong under-saturation in summer,
which is basically maintained by the stratification.
And then once the nutrients are gone and the summer turns into the fall
and winter season, the system starts to re-equilibrate,
and it comes via the fall situation, basically closer to the winter situation,
then basically the seasonal cycle starts all over again.
And then you can make your annual flux map if you want,
and you can compute uptake rates,
and everything which is yellow and cooler is an uptake,
and the orange colors in the southern part,
is a slight CO2 release from the atmosphere.
And this is sort of similar, what we predicted here,
that there are weak or closer neutral fluxes in the mixed area
and strong CO2 uptake, basically, in the stratified area,
and so this is what your annual map basically shows you.
And it took me or us quite a while to see that there's a little problem on the map,
and the little problem is basically this area,
and this is certainly a very well-mixed area in the North Sea,
but you can still see from the annual flux map that this is still an uptake of CO2,
and if you go back to the concept which I tried to explain you,
that there shouldn't be any significant fluxes in either direction,
you can see that this is a little bit of a problem,
because there's a fairly strong uptake,
and you can also see this, and this, I have to admit, took me also a while to see it,
that the area, despite the fact that it is shallow, is actually under-saturated,
and all of the rest of the mixed area, basically, is super-saturated,
and it is supposed to be, but the southeastern part, or the German bight,
or basically the part which is bordering by the European continental coast,
still reveals this under-saturation throughout the summer season,
and also presents itself as a sink of CO2,
which actually shouldn't be the case if we apply the concept of the stratified
with this vertically mixed area.
And since we cannot explain this with the DSC,
this would follow the pattern which we saw on the last slide.
In the end, you need to infer processes which can lower the PCU2
to maintain this under-saturation here,
and this is basically processes, essentially, which generate alkalinity,
because there's no other option than lowering the PCU to either take out CO2
or you increase the alkalinity.
These are the two players in the game,
and the DSC is not able to do this because it's a closed-loop system
without a massive net change.
So then you can plot, actually, alkalinity,
and you can see from the dates, this is about five or almost eight years
after the initial study, we started looking into this,
and so this map shows you basic alkalinity anomalies.
So if you make an annual average of the alkalinity distribution,
which shows you the left-hand side panel,
and then you would subtract each observation from the annual average
at any given point, you can give the anomalies,
and then you can see relative to the annual mean,
and then you can see more or less a weak fluctuation of alkalinity
in almost all of the nasty, except for the southern bite,
and in the end, this salinity-driven or dilution changes,
so they are not so massively strong,
but the big exception is actually the southern bite of the nasty,
where you can slightly increase alkalinity concentration in spring
and massively increase alkalinity concentrations in the summer,
and if you raise alkalinity, basically, you bring down the PCU2,
and this is actually what you see here,
so this is the same area where the PCU2 is far too low
for our nice little concept.
This is the area where also the alkalinity is released,
and the alkalinity cannot be released from,
or is not released from, in pelagic processes usually,
as long as oxygen present,
so in the end, we can predict that there has to be a sediment water column process
which causes this alkalinity to be high,
and in the end, is the primary cause for lowering the PCU2
and making the southern part of the nasty thing for CO2,
and also affects the pH system,
what we see in the later part, or the final part of the talk.
So the problem is, we can make a fairly safe guess
that this is not a pelagic problem,
because the pelagic system in ventilated areas usually is oxygenated,
and you cannot have processes, or anaerobic processes,
in aerobic water columns, so this doesn't work,
so in the end, we need to have an assessment
to approach sedimentary compartments,
and if you look at this map, there's basically two compartments available,
one is the shallow sediment,
and the other one is basically the vodency, or the sidewall,
or basically the edge of the north sea,
so it's the lateral and the vertical sediments,
if you want to call the vodency a lateral sediment, which play a role.
And so what we try to do is to identify those two sources,
and one option to do this very nicely,
and this is basically the last part,
it's now the thesis work of William Burt, which I initially mentioned.
We use the two radium isotopes,
because in the end, you can nicely attribute the sources of the isotopes
to the sediments, basically, so the vertical sediments
and the lateral sediments of the sidewall of the north sea.
And they are the parent isotopes of the radium,
as thorium and thorium is highly particle reactive,
so if there's a particle in the water column,
thorium will basically touch to it,
and it will sink, which means that the thorium is highly enriched in the sediments,
and so, of course, it's also the daughter of the thorium,
so the two radium isotopes are highly enriched in the sediments,
and their concentration in seawater are near zero,
because the source is the sedimentary one,
and then the half-life is usually short enough.
Now, there's another advantage of the radium as a tracer.
It's a seven-second group, metal ion,
so in the end, in a very plain textbook,
it doesn't do anything in the water column,
other than being transported or decayed,
so there's no biological interaction, no precipitation, and nothing else,
so it's a really very nicely physical tracer.
So the sedimentary sources are basically the rivers,
but also they are the bottom sediments,
where I talk about it, and the land-ocean boundary,
which in our case is basically the other word for what we see in the end.
And then, if you make a simple consideration about the decay times,
so the 224 radium has a decay time of less than four days,
and you can imagine that in three to four days,
you can't travel very much from the coastline,
and I'll show you on the next slide.
In the end, the 224 is an ideal tracer for vertical fluxes,
because if you see a radium in the shallow part of the north,
basically it cannot come from the land,
because it doesn't live long enough.
And the opposite is true for the 228,
it's an ideal tracer for the sidewall of one sea input,
because the release is near zero from the vertical sediments.
So we tried this in a little experiment,
so these are the distributions of the 224 radium and the 228 radium.
Please, again, keep in mind, the half-life is this of the 228,
it's been six years, so it really spends enormous time in the water column,
and the half-life of the 224 is somewhat less than four days,
so it survives really only a couple of days, and then it's gone.
And we basically made a very simple transport model
where we released radium from the coastline,
and then modeled how far it should last if it's transported away.
And the blue line is basically the output of the model,
and you can see that the 224 should be near zero because of the short half-life
a couple of tens kilometers away from the coast.
But the observations clearly are significantly above this ideal model line,
so in the end, the conclusion, which you can draw from it,
that the source of the 224 radium, which you can nicely see here,
is a sedimentary source and not a land-based source.
And this also explains somewhat of a stepwise function,
so basically the concentrations become zero in the northern part of the North Sea,
and if you look back into the depth distribution,
basically the switch from the blue and greenish colors to the purple colors
is exactly the line where you leave the well-mixed area in the south
and enter the stratified area,
and you don't see any radium-224 in the stratified area
because the diffusion time from the deep sediments is far too long,
and it just doesn't reach the surface layer.
So in the end, you can use the 224 very nicely as a sedimentary tracer
in ventilated waters from the vertical flux perspective.
And the opposite is basically true for the 228 radium.
This is a very long half-life. If you do the same modeling experiment,
you can nicely see that the concentration should slowly decrease
the further you move away from the coast,
and you can see that the blue line nicely matches our observations,
and you can see nicely also this in the distribution of the 228 radium
where the concentrations slowly decrease,
so the blue is still five disintegrations per minute, 100 liters,
so it's a substantial concentration which we can still see far away off the coast
because the half-life is long enough,
and this is basically the area where we don't see any 224
because the half-life is far too short.
So in the end, if you think about this,
we have two very nice tracers to address the question
for the southern bight, basically where the alkalinity comes from.
So if there's a nice coherent relationship with the 224 radium,
we can argue that this is a vertical or the benthic source,
basically which would be this area here,
and if you have a nice relationship to the 228, it is a coastal source,
so basically we have an input of whatever properties from the sidewall,
which in other words is basically the one seen in our case here.
I don't go too much more into detail for the 224,
but I would like to look a little bit more into the 228,
which is the input from the lateral side,
and if you now look at the concentrations of alkalinity and DSC,
which are the two big players in the CO2 system,
and you overlay them or compare them to the two radium distributions,
you can see clearly that the alkalinity is very enhanced in the southern part,
and this is in the end the distribution I showed you earlier as an anomaly.
This is now the direct observation from 2011,
and also you can see that the dissolved inorganic carbon is very much enhanced
in the land-sided area,
and this is a little bit of a surprise because usually you would think
the alkalinity function of salinity,
so the concentrations should go down with decreasing salinity,
so the concentration should both increase in direction to the open ocean,
but rivers have an effect of course with their concentration,
but there's also, this is a very strong indication that there is a DSC
and an alkalinity source basically in the southern ocean,
which reverses the trend which would mirror the salinity,
and this obviously is not there.
And again, the tricer which we use to separate
whether this is a vertical or lateral input are the two radium isotopes,
the 228 would be a lateral input, so this would be land-based input,
and the 224 would be a vertical input basically
from the surface elements of the southern North Sea.
And then we basically take the two plots which you saw
and focusing on the 228 for our lateral,
so if you plot the radium 228 against alkalinity,
you can see in the area which we are talking about,
so these are the southern bite samples
until the area where the stratification kicks in,
so this is about the samples south of the imaginary line here roughly.
And you can see there's a very nice relationship
between the alkalinity concentrations and the radium 228 concentration,
and this means in the end you can compute an alkalinity increase
or release per radium unit if you want,
and this is in the end the tool which we use
to quantify the alkalinity input,
and in case of the 228 it's the alkalinity input
which comes here from the land side.
And you can see that the radium 228 basically increases
if you go towards the shore or decrease if you go away from the shore,
and this is basically the line you have seen,
so this is your decreasing radium concentrations,
and you can then basically the next plot shows you,
okay, I see a radium of let's say 20 units here
and this corresponds to a certain alkalinity concentration
which has been released from the same source
and the radium has been released,
and this is basically the side wall of the water sea of the north sea.
So you get a linear regression,
and from the regression coefficient you can argue
that about 50% or so of the variability can be explained by the source,
so the radium 228 indicates that the lateral input
is about apparently one of the two processes
which supplies a certain amount of alkalinity,
and I'll give you the number on the next slide
to the southern part of the bottom sea.
And we can do the same thing with DSC,
we have to do a little bit of conversion of the DSC
to get rid of the salinity signal,
but in the end you can see here a biologically derived or metabolic DSC,
and this also nicely scales with the alkalinity
with the radium concentrations in the southern part of the north sea,
so this would be then the DSC concentration which are high here
and then decreases basically in the same direction like the radium decreases,
and so you can see that with high radium concentration
you can see high metabolic DSC concentrations
and they nicely decrease basically the further you go away,
this means you dilute the signal if you go in the open north sea.
So this is basically then the step to the quantification
of the lateral carbon and alkalinity input,
and the interesting thing, and this is basically where we started earlier,
is that both of them increase, and if you would have a pelagic system
you shouldn't see anything, this would be blank basically,
there shouldn't be any alkalinity release
if you have a pelagic or an oxygenated system,
and so this is clearly a very nice indication
that there's an anaerobic system which releases both the DSC
and the alkalinity in parallel,
and by this alters the buffer system as required basically
to explain the low PCU2 and high pH ratios in the southeastern corner.
And then you can, from this you can draw them up if you want
and then integrate this over the water column,
and then you can see basically what you expect that the alkalinity input,
so this is a net flux which is computed now from the radium concentration,
increases if you go away from the coastline,
so you basically release your alkalinity in the area
and then it's diluted into the open north sea,
and you can see the same with the DSC, higher concentration on the coastline,
and then the further you move away from the concentrations
or the inter-inventories basically decrease.
And then you can make some sort of estimate about the concentration
and what the range of importance is,
and basically the input of the alkalinity is what we computed here
is between in the order of 10 to almost 50 micromoles per kilo,
and this is A in the range of the seasonal variability,
so it's a fairly big signal compared to what we seasonally,
and also a recent study by Fabian Zwichtenberg here in Hamburg,
he did this with a modeling approach
and he came up basically with the same number or the same order of magnitude at least.
And similar range of magnitude we observe for the CO2 release
or metabolic CO2 release in the water sea,
and the signal basically corresponds to about 10 to 40 micromoles,
so similar to alkalinity.
And this is again well in the range of the seasonal variability of the DSC in the area,
so in the end it's a massive contribution to the seasonality of the carbon system,
in both cases alkalinity and the disease of inorganic carbon.
And then you can think about the ratio of those two,
and this is basically the special thing which points to the anaerobic processes
and the particular identification here.
So the ratio of those two is about one,
and this is what you usually assume for identification
that you have identification releases,
one unit CO2 and one unit alkalinity.
And if this would be an aerobic system,
basically this ratio is minus one over six,
six minus one over seven,
so it's very basically the alkalinity release in aerobic system is basically zero,
so again this map would be wide if you would have an aerobic system.
But the ratio one roughly clearly shows you that this is an anaerobic source
and identification is one of the primary processes which does this,
because in the end it's reversible,
and filtrate reduction is not necessarily reversible.
And the source in this particular case is again is the Voden C,
and we know very well that the Voden C is a very anaerobic system,
we start scratching with our finger and the sediment,
you can smell it nicely that oxygen is lacking there,
and you have lots of hydrogen sulfate in other products which you can see,
and it's both see and smell.
So then you can do one trick,
and this brings us to the final idea of eutrophication and ocean atrophication,
you can pretend that basically the CO2 release would be an aerobic one.
So what you do in your, or we did in our computation,
where we set this value basically to zero,
and assume that the overall metabolic release of CO2,
which is shown on this part, is a purely aerobic one.
So this would be the pelagic oxygenated system,
where respiration of organic matter only releases CO2,
but that doesn't touch the alkalinity system.
And then in the end you remove the additional buffer effect,
which the alkalinity releases,
and you can see a fully CO2 controlled response of the pH and the CO2
as compared to both CO2 and alkalinity controlled response,
which is a real situation in this area.
So if you take away the alkalinity release in the end,
this means you add quite a substantial number of protons basically to the system,
because the alkalinity basically absorbs the protons,
and the proton release, which is computed here,
is basically an assumed aerobic respiration situation in the Vodency,
which is not present,
but it shows you very nicely what the alkalinity release does to the pH.
Because if you would add your alkalinity,
basically you lower the concentration of the proton
by exactly the amount which is shown on the map,
and the pH goes massively up by the alkalinity release,
and the opposite does the PCU2.
The PCU2 goes down massively by the parallel release of alkalinity and TSC.
And this is in the end exactly what we saw in the...
Yeah.
This is in the end exactly what we saw in the beginning,
in the area of the southern North Sea,
that we had to bring down the PCU2 basically in this area,
and this is simply not possible.
So if we start releasing CO2, the pH goes down.
But if we start adding alkalinity basically,
exactly the units which are given as numbers absorb alkalinity,
and the pH actually goes up, and the PCU2 goes down.
And the effect on this area is, again,
well in the range of the annual or seasonal variability.
So if you do this sort of experiment,
you start decreasing the pH by the number which is given here,
and if you look at reports from pH changes over the past decades,
so the provost reported from the northern North Sea,
it's about 0.2 units per year,
and the open ocean effect of 10 lower.
So the effect on the pH in the PCU2 is massive,
and this is, again, a reflection of what we saw earlier,
that the PCU2 is massively lowered by this alkalinity release.
So what I want to do, this basically brings us back to the interaction
between human beings and coastal ecosystems,
or coastal biogeochemistry,
and it's a very nice and tight coupling,
or at least an idea, or I would suggest an idea,
how to couple the unification, the denulfification,
and basic ocean authentication,
which is some sort of human dimension added.
And these are all data basically compiled from the Dutch coastline,
coastal coastline, where the provost,
they went into the all available databases
and plotted the pH for the near-course stations.
So the pH data, I'll show you on the next slide there,
somewhere from this area here.
Some are Dutch territorial waters from Reichswatterstad
and other databases.
And the upper slide basically shows you the changes of the system
between September 1977 and September 1984,
and the black underlying line is basically nitrate runoff,
which comes here from the Hamburg database from Johannes and Herman.
And you can see two very nice things.
A, the pH has a positive gradient in this area from the late 70s and mid 80s,
so the pH increases by 0.02 units per year.
And you can also see that this is a nice period
where the nursery was strongly unified,
that basically the nitrate river runoff basically constantly
or must have basically increased in this time.
And if you remember what the open ocean gradient should do,
the open ocean gradient of the pH is minus 0.01 or 0.03 units per year.
So what we see in the water is just the opposite of the,
in the southern north is just the opposite,
what you would expect from the rising atmospheric CO2 concentrations.
So pH goes up basically and nicely parallel to the increase of the river runoff.
And then suddenly European Union member states,
they thought this is not a good idea, we should stop the unification
and should stop the nitrate release by the rivers.
And this happened basically in the period somewhat later.
And the bottom panel shows you the nitrate and pH data basically from 1998
until September 2005.
And you can see that basically European relations
nicely showed their cause, their effects.
So the nitrate runoff basically constantly decreases over these almost 10 years.
And the same thing does the pH.
So the same, the pH decreases, decrease in the same period of time.
And it's a factor of 10 higher the decrease than you would expect
from the open ocean situation which is only imprinted by the atmosphere.
So what we see here in the end, it's a, what is implied here,
is a very strong relationship between the nutrient runoff and nitrate runoff
and the pH change in the system.
So the pH increases with increasing nitrate
and the basically pH decreases with decreasing nitrate.
And in my view, the only, or one of the major ways basically to explain this
is to invoke alkalinity which is directly regulated basically
by the nitrate runoff from the rivers.
So what the common mechanism, and if you don't have sedimentary interaction
in your model, you won't see it.
But also other observations or ideas show that in the end,
the argument can be made that if you increase the nitrate,
basic production will go up and absorbs CO2.
So this would cause your pH to increase.
But on the end, and you can see this nicely on the past slide,
in winter when biologic is basically, has a sleeping period,
the pH CO2 will equilibrate with the atmosphere again.
So that's very difficult to explain a standing stock change of the pH
and the DSC if you only play around with production
and CO2 uptake and release.
And you nicely see this basically here, there's lots of wiggles,
but you see nicely the underlying pH here,
which is the production respiration cycle which I have discussed earlier
as a means of the PCU2.
But what you can actually do in addition to change the production,
you can also denitify and release alkalinity.
And if you start increasing your nitrate runoff from the rivers,
basically you increase your alkalinity production via denitification.
So you increase the buffer capacity,
and this means you raise the pH basically in the end
because you increase denitification.
This is actually what you see here in my view.
So that the runoff denitification
basically does trigger massive amounts of denitification
and to a degree basically that the pH actually
overturns the atmospheric signal and gets in an increasing situation
because of the very, very strong alkalinity released
due to the nitrate reduction or not nitrate,
due to the denitrification of nitrate.
And then if you take away the buffer capacity,
of course the pH will decrease if you start manipulating the water.
And this is what you see in the more recent years
that for good reasons we reduced the nitrate release to the rivers.
And then basically you constantly take away the alkalinity,
decrease the buffer capacity,
so the surface oxygen suddenly picks up the atmospheric signal,
but because the alkalinity reduction is so strong,
the pH drops much faster than the atmospheric signal prescribes.
And the reason is that basically through the alkalinity standing chop change,
you will change the ratio between the pH change and the PCU2 change,
which in common words is you lower the buffer capacity.
So what we do in the end is basically we make the biutification,
you could say or argue that we make the oceans more vulnerable to ocean authentication,
but of course this is a desired effect to get rid of the nutrients.
But the problem, and this is where the human beings again come into play,
that this period here nicely shows you the decline of nutrient input,
but there are ongoing processes and one of them is the biofuel production,
which has the potential to reverse this, or you go to a trophification trend.
So what's happening in the future? I'm not sure.
I don't know whether anybody is.
So as a conclusion, since Johannes is coming closer,
so we thought about that basically if you have an aerobic system
or if you have an open ocean system,
in the end the PCU2 and the pH are strongly controlled by CO2 driven changes.
So this is productivity and temperature largely,
so it has a very, plays a role, but it's very stable and doesn't vary much.
So in the end the whole system is very much CO2 controlled.
But this didn't work, this whole concept basically if it came closer to the coast.
And we needed to invoke an alkalinity altering processes on a seasonal scale
to explain the CO2 variability.
And we did this basically using the two volume isotopes
and exploited basically their very different half-lives.
And then basically eventually the interaction with the surface sediments
and the latency supply alkalinity,
and this is basically nothing else than enhancing the buffer capacity
so the PCU2 goes down and the pH goes up over time and over season.
And this is what we saw both in the CO2 system and in the pH.
And then the last step basically which I talked about at the end
is basically that the anthropogenically driven,
in particular nitride runoff has a very strong impact in the coastal area
on the actual alkalinity production and directly affects CO2 fluxes
but also alkalinity in very well-ventilated waters if the population is high enough.
Thank you.