Sources & Sinks: A Tale of Coastal Biogeochemistry - BONUS COCOA
Equipment explained: part IV - the HAPS corer
This post might as well be entitled “Ode to HAPS”. For one thing, the HAPS corer is by far my favorite sediment sampler, clearly deserving of being sung about. For another thing, it already has been (cruise internally) sung about, showing that not only I have a personal affection for it, but that it is popular among several COCOA people (aka the HAPS gang).
So what is this HAPS sampler and what is so special about it?
The HAPS is a sediment corer for coarse sediments, i.e. sands. The tricky parts with sand sediments are that they are quite hard and sturdy, and that they have big pores, which impose only weak cohesive forces onto the pore water. This can result in water actually flowing through the pore space of sand (advective pore water flow), which has everyone experienced who ever saw a wave washing up a beach…and then disappearing into the sand under the own feet.
Pore water flow has huge implications for organic matter turnover, sediment biogeochemistry, and general elemental cycling- however, in terms of sampling, it means particularly one thing: how not to lose the pore water during core retrieval, if it´s so mobile? (In more plain words: pore water flow in sand is scientifically and ecologically really cool stuff, but it does add a challenging element to undisturbed sampling of sand sediments).
Luckily, there is the HAPS!
We wondered for years, what its name stands for (maybe “happy and prosperous sampling”?!), until getting the answer from the inventors themselves (Kanneworff & Nicolaisen 1973): apparently, “haps” is a Danish exclamation used when something is grasped very quickly. And that´s exactly what the HAPS does: after coring, a tight top lid keeps the sediment in the core, and during core retrieval, a super sharp, quick and tight shovel cuts immediately under the sediment core, so that pore waters are kept where they belong- in the sediment. However, never forget to use the core lid, otherwise also the super quick shovel does not help in holding any sample (*learned from experience*).
This sounds like basic sediment coring theory. Yet, the difference of the HAPS to e.g. the GEMAX corer is its weight, its stability and the speed of its closing mechanism.
Like the GEMAX (Equipment explained: part II - the GEMAX / GEMINI corer), HAPS is basically a gravity corer, i.e. it cuts into the sediment based on its own weight. But even if GEMAX does feel heavy when loading it onto the ship, it is too light to be able to cut into sand sediment. Plus, sands are usually located in high energy environments (too turbulent for finer particles to settle), where samplers need to be heavy to go down the water column and onto the sediment surface without being drifted away. The net weight of a HAPS corer is ~ 100 kg, which can be added up by additional 60 kg of lead weights, and a square bottom frame supports high stability at the sea floor. It is made out of stainless steel, including the core barrel and the closing shovel, which are both sharpened for uncompromising sediment penetration. If the weight of a fully loaded sampler should still be too light to penetrate the sediment, it can be equipped with a powerful vibrator unit. Insider tip: don´t drive it for too long, you might anchor yourself in the seafloor.
Undisturbed samples are easily to be seen in the clear water phase on top of the sediment, which during our sampling at the Finnish coast sometimes also included Saduria sp., having been surprised by the quick sampling (Killing in the name of).
Well, HAPS got its name for a reason.