Where do the NSW numbers come from?

[HuduVudu]

We get the numbers that are considered "NSW".

e.g.
Alk 7.7
Ca 420
Mg 1270

Those are my basic understanding of what is generally considered "NSW".

As to the original question where do these numbers come from? Are they an aggregate or average? Are they from a specific area of the ocean like say the fore reef?

Curious as to where these numbers come from because my ocean water collection is showing something dramatically different. I am trying to see if there are other factors involved. Perhaps seasonality or tides.

One interesting thought though is that the Alk is dead on each time that I test at 7.7dKH. This is confirming my growing understanding that the Alk should not change ... not even a little bit.

Thanks in advance for any help.

 

[blaxsun]

Well, I saw a R2R thread where a guy collected some NSW samples from the Caribbean and got 7.3 for alkalinity, 400 for calcium and 1440 for magnesium - so I think that depending on region and other factors these can and do vary, as you suggest.

What works in the ocean and works best in our reef tanks is something different entirely.

 

[Lyss]

We get the numbers that are considered "NSW".

e.g.
Alk 7.7
Ca 420
Mg 1270

Those are my basic understanding of what is generally considered "NSW".

As to the original question where do these numbers come from? Are they an aggregate or average? Are they from a specific area of the ocean like say the fore reef?

Curious as to where these numbers come from because my ocean water collection is showing something dramatically different. I am trying to see if there are other factors involved. Perhaps seasonality or tides.

One interesting thought though is that the Alk is dead on each time that I test at 7.7dKH. This is confirming my growing understanding that the Alk should not change ... not even a little bit.

Thanks in advance for any help.

Out of curiosity what are the numbers you’re getting? I’ve always wondered about this tbh.

 

[HuduVudu]

@Lyss
From the Gulf of Mexico near Corpus Christi:
Alk 7.7
Ca 350
Mg 970

Turns out the specific gravity was 1.022 so I am getting some fresh water run off from some where. I didn't see any rain, and we haven't had a bunch of rain, so I am not sure where this was coming from. I collected last year and the Ca was 400 and Mag was 1200. I don't remember what the specific gravity was.

 

[JimWelsh]

For all major constituents: https://www.ocean.washington.edu/courses/oc400/Lecture_Notes/CHPT4.pdf

For alkalinity: https://www.ncei.noaa.gov/access/ocean-carbon-data-system/oceans/Dickson_CRM/batches.html

It's very difficult to dispute Pilson's numbers, based on the large data set and the rigorous nature of the work, various anecdotes notwithstanding. Note that the g/kg units should be multiplied by 1024.763 (1000 to get from g/kg to mg/kg, then the density factor at 20C of 1.024763 to get from mg/kg to mg/L) to get mg/L at 20C. Use 1023.363 (different density factor) for 25C.

Similarly, it is very difficult to dispute Dickson's work. In this case, take the alkalinity in micromoles/kg, divide by 1000 to get meq/kg, multiply by 1.024763 at 20C (or 1.023343 at 25C) to get meq/L, then (optionally) multiply by 35 and divide by the salinity to normalize to S=35, and finally, multiply by 2.8 to get from meq/L to dKH/L. Note that the alkalinity very consistently turns out to be around 6.6 dKH/L EDIT: When normalized to S=35.

 

[Randy Holmes-Farley Verified Community Expert]

I agree that the major and minor ion concentrations in seawater (as a function of salinity) are very well understood, and the alk value in the first post is too high for NSW.

The book "Chemical Oceanography" by Millero has many pages of discussion of the concentrations of ions, including when and how they vary. I used it for all of the values in my article on seawater:

What is Seawater? by Randy Holmes-Farley - Reefkeeping.com