Hoernle, Kaj

OceanRep

  SO-255  Vitiaz 6. Weekly Report (03.04. – 09.04.2017)  R/V SONNE  34°26´ S / 178°54´ E  During the sixth week of the cruise, we carried out our last sampling profile across the Kermadec Arc and Havre Trough, including sampling of the Kermadec and Colville Ridges.  After completing the sampling of the Hangaroa Volcano in the volcanic front early Monday morning, we spent the next two days traversing the Havre Trough along a NW-SE sampling profile. We sampled the margin of a 4000 m deep basin, several NE-SW trending ridge-like structures and some small cones. Wednesday was spent sampling the deeper portions of a rifted scarp of the Colville Ridge. Then we crossed the Havre Trough again sampling more basin margins, ridges and small, sometimes perfectly conical, cones, ending at the Kuiwai volcanic front stratovolcano, which we sampled at three different sites on Thursday. The next day we dredged several volcanic cones south of Kuiwai. On Saturady we carried out three dredges at different locations on the Ngatoroirangi stratovolcano and then successfully dredged the deepest margin of a nearby 4000 m deep basin. Saturady night, we recovered a nice array of mafic samples from two cones on the Kermadec Ridge, as well as a nearly full dredge of fresh lavas from deeper on the Kermadec Ridge itself. Our final dredge of the cruise was carried out Sunday at noon on the Sonne stratovolcano, named after the old R/V Sonne, which unfortunately was empty. Nevertheless, 83% of all dredges conducted on the cruise recovered hard rocks and thus the overall sampling was very successful. The three major goals of the cruise were to sample the Havre Trough, Colville and Kermadec Ridges (former Vitiaz Arc) and the Kermadec forearc. We were very successful at sampling the full variety of structures in the Havre Trough between 28-35°S, recovering a wide array of fresh lavas and pumice ranging from mafic basalts to rhyolites. Sampling of the Kermadec and Colville Ridges between the aforementioned latitudes was also successful, bringing up a large variety of lavas and volcaniclastic rocks. We had the least success at recovering volcanic rocks from the forearc, where most dredges contained mud or sediments despite dredging on very steep slopes, suggesting that the southern Kermadec forearc is largely accretionary. All in all, we recovered more than enough material for the three doctoral students on board (two German and one Japanese) to successfully carry out their doctoral studies. The zooplankton sampling goals were achieved through the collection of three vertical net hauls and four oblique net tows. Over 6900 specimens of planktonic gastropods from 37 species were collected, providing abundant material for future morphological and molecular analysis. Atlantids were also successfully maintained under laboratory conditions and pilot ocean acidification experiments were carried out, providing a foundation for future studies. The microbiological experiments and underway samplings were finished successfully. Huge amounts of sample vials are now packed and prepared for shipping to Kiel. Sunday evening we celebrated the successful end of our work program, several birthdays and the retirement of one of the ship’s crew by grilling on the deck and a small party. The cruise will end three days early, so that the winch holding the deep-sea cable can be fixed before the next cruise. All on board are doing well and are looking forward to reaching Auckland.   Kaj Hoernle and the SO255 scientific crew  	 	Emptying	 one	 of	 the	 last	 dredges	 of	 the	 cruise	 also	required	a	bit	of	footwork.	Scientists	 on	 the	 night	 shift	 loading	 the	 samples	into	boxes	for	sawing	and	describing	in	the	lab.	 	 	Grilling	on	deck	to	celebrate	the	end	of	a	successful	cruise,	 several	 birthdays	 and	 one	 of	 the	 crew’s	 last	voyages	before	retiring.	Our	 five	 star	cook	enjoying	 the	party	after	making	sure	that	everyone	got	more	than	enough	to	eat.	 	SO255	scientific	crew:	Can	you	guess	who	missed	the	photo	shoot	and	had	to	photoshop	herself	into	the	picture? 

6. Wochenbericht SO255 Vitiaz

  SO-255  Vitiaz 1. Weekly Report (01.03. – 05.03.2017)  R/V SONNE  34°14´ S / 178°27´ E  On the R/V SONNE cruise SO255 (Vitiaz Project), we are investigating the Vitiaz-Kermadec subduction system, which extends from the Taupo Volcanic Zone on North Island of New Zealand for ~1300 km to the Tonga subduction system (see figure on next page). Here the Pacific Plate subducts (sinks beneath) the Australian plate, which among other things leads to strong earthquakes and frequent volcanic eruptions. The present-day Kermadec-Tonga Arc systems and Colville-Lau Ridges formed by splitting of the older Vitiaz Arc. Thereafter rifting and seafloor spreading formed the Havre Trough and Lau Backarc basins. In collaboration with scientists from New Zealand, the U.S.A., Japan, Switzerland and England, the SO255 cruise will conduct extensive bathymetric mapping, sub-bottom, magnetic and gravity profiling, and hard-rock sampling (via dredging) to investigate the physical and chemical conditions that control the development of subduction zones, including subduction initiation and evolution, and the transition from arc splitting to backarc basin generation. Smaller biological studies will complement the geological program. On March 1, most of the scientists boarded the ship and began unpacking the equipment and setting up the laboratories in preparation for the cruise. After the boarding of some additional technical personal and a member of the funding agency, we set sail on the afternoon of March 2 from Auckland. The weather was gorgeous as were the views of downtown Auckland and the surrounding bay. The bay was so filled with sailing vessels that the captain often had to blow the ship’s horn to make a path through them. After a day of carrying out successful tests on the ship’s sonar system, the Sonne returned to Auckland to let off the technical personnel. We also took a last scientist on board who had to postpone her trip due to illness. Saturday afternoon the Sonne again left the Auckland harbor to officially begin the SO255 cruise. Around mid-day on Sunday, we arrived at our first workstation and began our scientific program with three successful dredges on and near the Colville Ridge.   All on board are doing well and send their greetings.  Kaj Hoernle and the SO255 scientific crew   	 	Downtown	Auckland	from	the	Sonne	(Kaj	Hoernle)	 Goodbye	Auckland	(Kaj	Hoernle)			  Bathymetric map from the Tonga-Kermadec Arc (Christian Timm) 	

1. Wochenbericht SO255 Vitiaz

  SO-255  Vitiaz 5. Weekly Report (27.03. – 02.04.2017)  R/V SONNE  32°47´ S / 179°30´ W  During the first part of this week (Monday through Friday), we sampled volcanic structures within the Havre Trough between 29–31°S latitudes. All of the sampling was carried out in the eastern half of the Havre Trough due to the western half consisting primarily of large sediment-filled basins and smooth basement morphology. In contrast the eastern half of the Havre Trough contained abundant small cones and ridge-like structures, as well as some grabens with steep walls, that were successfully sampled by dredging. The most spectacular discovery of the week is what appears to be a volcanic structure (possibly dome field) with a caldera >2 km in diamater in the middle of it (see photo). The caldera has resurgent domes in it, formed after collapse of the caldera floor. The caldera is located about 50 km behind the Macauley Volcano, which also has a large caldera and is located at the Kermadec volcanic front. Although calderas are common on the volcanic front in this region, none have been previously discovered this far in the backarc. The Giggenbach volcanic field, consisting of a half dozen large volcanic cones that we sampled two weeks ago, lies between Macauley and the dome field with caldera. The dome field is located at the intersection of NE-SW and ESE-WNW trending ridges, presumably formed through magma rising up along faults in the backarc basement. Two dredges were carried out on the inside caldera walls and two on domes outside the caldera. Most samples were dacitic to rhyolitic but some samples from outside the caldera appear to be andesitic. Thereafter we sampled NW and NE of the Havre Volcano, which erupted in 2012 forming pumice rafts that reached Australia and Tasmania one to two years later. We were surprised despite our proximity to Havre Volcano that many of the dredges didn’t contain any of the Havre pumice, despite the pumic raft having passed over these structures. On Saturday we began dredging on the Kermadec Ridge (between 31-33°S), in order to get older samples predating the splitting of the Vitiaz Arc into the Kermadec and Colville Ridges. We recovered a mix of volcaniclastic rocks and fresh lavas with varying amounts of plagioclase, clinpyroxene and olivine phenocrysts. A small cone on the western side of the Kermadec Ridge produced ankaramitic lavas with up to centimeter-sized chrome diopside crystals, similar to a cone near Kibbelwhite Volcano sampled during the first week of the cruise. Thus far 82.8% of the dredge hauls on this cruise were successful. In order to calibrate the SIMRAD multi-beam system used for mapping the seafloor to find appropriate sampling sites for dredging, CTD (conductivity-temperature-depth) acoustic profiles were made through the water column.  Biological oceanographers are studying samples taken with the CTD to study degradation processes in the deep sea to depths of 4000m. Bacteria, which play a key role in the marine carbon cycle, degrade the majority of the organic carbon that is photosynthetically fixed by microalgae in the surface ocean. However, a certain fraction of the organic matter is refractory in the deep sea. In order to understand why bacteria do not degrade these compounds, the biologists are running lab experiments and sampling the water column to determine the concentration and composition of the organic matter controlling the bacterial degradation processes. On board, the deep sea water is incubated under various test conditions for 30 days in bottles and sampled at regular intervals. The collected samples will then be analysed for bacterial growth, carbohydrates, amino acids, gel particles and other biogeochemical parameters in the laboratories at GEOMAR. Although the weather this week reminded us of northern Germany (overcast and rainy) and the seas were somewhat choppy, the sun came out again and the seas calmed to provide us with a beautiful Sunday! All on board are doing well, although somewhat exhausted – the price of the successful dredging this week.  Kaj Hoernle and the SO255 scientific crew  	 	Volcanic	structure	with	2km	diameter	caldera	 in	 the	middle	and	younger	resurgent	domes	in	the	caldera.	Both	 inner	 and	 outer	 walls	 of	 the	 caldera	 were	successfully	dredged.	A	 dredge	 from	 the	 Kermadec	 Ridge	 with	 large	blocks	 of	 volcaniclastic	 rocks:	 the	 beginning	 of	 a	long	night.	 	 	The	 blocks	were	 so	 large	 that	 it	was	 difficult	 to	 pry	them	out	of	 the	chain	 sack.	Scientists	patiently	wait	in	the	background	to	get	to	the	rocks.	After	more	 than	20	minutes,	 just	one	 last	boulder	to	pry	loose.	 	 	Playing	with	 fire	on	a	 rocking	ship:	 	Biologist	sealing	glass	tube	containing	seawater	sample.	Brewing	up	some	magic	potions?	No,	bacteria	from	seawater	samples	were	being	dyed	and	filtered.		 

5. Wochenbericht SO255 Vitiaz

  SO-255  Vitiaz 3. Weekly Report (13.03. – 19.03.2017)  R/V SONNE  28°27´ S / 177°39´ W  Monday through Thursday of the last week was spent attempting to sample the area between the Kermadec arc and deep-sea trench (forearc). Dredges were carried out at depths of up to 8800 m in the Kermadec deep-sea trench, being the deepest dredges thus far with the new (and probably also old) Sonne. Unfortunately most of the dredges only brought up consolidated mud, reflecting sediments accreted to the forearc. Three dredges however recovered a variety of rocks ranging from diorite and a variety of plagioclase phyric basalts to sediments with abundant small volcanic clasts. Some clasts were oxidized bright red pointing to derivation from a subaerial arc volcano. Overall our forearc dredging confirmed the hypothesis that accretion is the dominant process when the deep-sea trench is sediment-filled.  On Thursday we returned to the Kermadec Arc and carried out three successful dredges on the west-facing faulted scarp of the Kermdec Ridge, which should provide further insights into the earlier history of the Kermadec/Vitiaz Arc system. Then we proceeded to the Giggenbach seamount cluster, named after a German geochemist. We successfully sampled five seamounts, recovering large amounts of basaltic to dacitic lavas and pumice. Some of the pumice showed beautiful evidence of mingling between basaltic and dacitic magmas, indicating that both were liquids when they came into contact. The injection of basaltic magma into a dacitic reservoir was most likely the trigger of the explosive eruption forming the pumice. Some of the pumice appears to be very young and is certainly related to the eruption of the submarine Havre Voclano in 2012, which created a huge blanket of floating pumice, covering an area twice the size of New Zealand within three months. Moved by the ocean currents, the pumice blanket reached the beaches in Sydney in 2013 and those in Tasmania in 2014. Of the 59 dredges thus far, 44 (=75%) successfully recovered hard rocks. For much of the week, the weather was windy and seas rough, sending a number of scientists to their bunks. Almost as if planned, the winds died down, the sun came out and the seas calmed for the Bergfest (mid-cruise party). Although a few days early, the opportunity for the Bergfest was provided by the necessity to map several profiles across the Havre Trough and along the Colville Ridge to identify future dredge sites. We also used the break in dredging and laboratory work to switch the day and night shifts.   All on board are doing well, having recovered from the windy weather and the Bergfest, and send their greetings to those at home.  Kaj Hoernle and the SO255 scientific crew  	 	Grilling	 on	 deck	 during	 the	 Bergfest	 (mid-cruise	party).	(Nina	Hinz)	Delicious	fruit	plate	at	the	Bergfest.	(Nina	Hinz)		 	 	Sawing	rocks	is	a	wet	and	dirty	job.	(Kaj	Hoernle)	 Lots	 of	 great	 side	 dishes	 to	 go	 with	 the	 grilled	steaks,	pork,	lamb	and	salmon.	(Nina	Hinz)		 	 	Wouldn’t	you	like	to	have	this	wrench	set	at	home	in	your	workshop.	(Kaj	Hoernle)	Who	 says	 that	 describing	 rocks	 isn’t	 fun?	 (Kaj	Hoernle)		 

3. Wochenbericht SO255 Vitiaz

  SO-255  Vitiaz 4. Weekly Report (20.03. – 26.03.2017)  R/V SONNE  28°57´ S / 179°33´ W  The beginning of the week was spent sampling our northernmost profile of the study area between c. 28-29°S latitudes. The sampling was very successful on the Kermadec Ridge and in the eastern and younger portion of the Havre Trough. We were even able to sample the Havre Trough basement by dredging one of the fault scarps forming a graben wall. Although all cones on the eastern side of the Trough produced fresh samples, we only recovered mud from the cones on the western side, indicating that they were older and covered by marine sediments. Next we sampled a fault scarp on the Colville Ridge and a guyot seamount west of the ridge. Guyots are flat-topped, steep-sided, conical volcanoes, which in most cases once formed ocean island volcanoes. After the volcanic activity ceases, the tip of the volcano is eroded to sealevel.  As the crust beneath the volcano cools, it subsides below sealevel. On Tuesday the dredging came to a halt due to problems with the deep-sea winch. As a result we spent the next two days mapping areas of the Colville Ridge in preparation for dredging. Early Thursday morning, we were able to resume dredging of the Colville Ridge and seamounts west of the ridge. Recovering relatively fresh volcanic material has proved challenging, because most of the samples are volcaniclastic, made up of small fragments of often altered voclanic material. Nevertheless, we have recovered some relatively fresh lavas and some of the larger voclanic fragments in the clastic rocks are relatively fresh and can be used for age dating and geochemical analyses. In addition to the geological studies, we are also sampling zooplanton with a planton net. This week we carried out our fifth and most successful deployment of the planton net. A huge variety of planktonic creatures and large numbers of our target group, swimming gastropods (snails) known as pteropods and heteropods, were recovered in the net. The latest catch included over 1700 swimming gastropod specimens of 27 species. We can now begin to explore the potential of using living heteropods in laboratory studies of changes in the ocean environment, something that has not yet been considered in the recent influx of ocean acidification research. The weather for most of the week was gorgeous and the seas very calm, like the surface of a lake. The nice weather has been accompanied by many beautiful sunrises and sunsets (see photos) and provided the opportunity to test the life boats.  All on board are doing well:  Working hard and enjoying the nice weather and calm seas.  Kaj Hoernle and the SO255 scientific crew  	 	The	beginning	of	another	day	on	board.	Sunrise	from	the	cafeteria	during	breakfast.	(Kaj	Hoernle)	Taking	 advantage	 of	 the	 calm	 seas	 to	 test	 the	lifeboats.	(Kaj	Hoernle)		 	 	Fishing	for	zooplankton:		Deployment	of	the	plankton	net.	(Debbie	Wall-Palmer)	Sometimes	it	only	takes	one	rock	to	fill	the	dredge.	(Kaj	Hoernle)		 	 	Heteropod	 Atlanta	 echinogyra	 (zooplankton).	 Since	these	small	mm-sized	creatures	have	eyes	and	try	to	avoid	being	caught	in	the	net,	the	net	is	towed	at	~4	km	 an	 hour	 so	 they	 cannot	 escape.	 (Debbie	 Wall-Palmer)	The	end	of	another	successful	day	on	board.		(Kaj	Hoernle)		 

1. Wochenbericht SO255 Vitiaz

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