The Baltic Dry Index (BDI) is an economic indicator issued daily by the London-based Baltic Exchange. Not restricted to Baltic Sea countries, the index provides "an assessment of the price of moving the major raw materials by sea. Taking in 23 shipping routes measured on a timecharter basis, the index covers Handysize, Supramax, Panamax, and Capesize dry bulk carriers carrying a range of commodities including coal, iron ore and grain.".
Not much of an traffic there: https://www.marinetraffic.com/
Forget about the BDI Lobster (I'm a freight trader), the market is fundamentally fucked for another 18 months on massive oversupply (and banks are tied to shipowners to massive debt) but it doesn't mean trade flow will shrink. The fleet supply will exceed the demand but the demand is still gonna grow (moderatly). At such low levels the BDI couple triple it wouldn't change anything for the global economy. For marine traffic it's using land stations and does not use AIS data (ship own positioning distributed via satellite) so you won't see a 5th of the traffic on this.
No problem:p Linking traffic to global economy is tough, it's so scattered and specialized:p One thing to monitor (and it's been collapsing) is chinese hunger for raw materials such as coal and iron ore. China switched its coal policy as it is by far the largest largest producer and never really needed to import any (they simply cut their imports by more than 50% in a year). As far as Iron ore is concerned (the biggest flow on water) it's stabilizing after 2 years of extreme growth. China has been creating big IO stockpiles but its steel consumption (which has been the best indicator of chinese growth in the last decade) has been turning south and is showing concern about infra+property markets. In other words global trade flow growth has been shrinking. Now the question is, how long will it take for china to transition into "consumer economy" such as the US and not an "investing/infrastructure economy" has its been the case for the last 20 years. My feeling is that China was the motor of the commodity boom from 2003 onwards which fueled global growth, but will not be as commodity supportive for the next decade; depending on how quickly they turn into a service based economy will tell us the truth